Severide (Taylor Kinney) and Stella (Miranda Rae Mayo) are on the lookout for a very unstable Grant (guest star Guy Burnet), who left Chicago Med without notice. Now that Dawson (Monica Raymund) is responsible for Louie, she questions her dangerous career path as a firefighter. Casey (Jesse Spencer) continues his work as Alderman but his relationship with his political consultant, Susan Weller (guest star Lauren Stamile), cools. Problems continue for Borrelli (Steven R. McQueen), who still blames Chief Boden (Eamonn Walker) for the death of his brother, and the situation reaches a boiling point. Meanwhile, Mouch (Christian Stolte) and Brett (Kara Killmer) start off on a new venture together.

Casey (Jesse Spencer) and Dawson (Monica Raymund) find themselves unexpectedly caught in the middle of a potential political mess. Stella (Miranda Rae Mayo) is left to make a serious decision about her ex-boyfriend. While responding to an auto accident, members of truck and squad find themselves in the middle of a dangerous situation. Elsewhere, Severide (Taylor Kinney) befriends a famous socialite (guest star Scott Elrod) that might distract him from his duties at 51, while Brett (Kara Killmer) and Mouch (Christian Stolte) set aside their writing differences for the greater good.

Casey (Jesse Spencer) enlists Susan Weller (guest Star Lauren Stamile) to help with an urgent personal matter. Severide (Taylor Kinney) receives an offer to travel luxuriously with rich party guy Travis Brenner (guest star Scott Elrod) and Stella (Miranda Rae Mayo) uses all her resources to help a sick street kid after saving him during a tunnel fire. Meanwhile, Otis (Yuri Sardarov) and Herrmann (David Eigenberg) discuss their concerns over Molly's lack of customers.

While checking out a warehouse as part of his Alderman's duties, Lt. Casey (Jesse Spencer) finds himself in a bad spot when a forklift accidentally pierces a tank storing acid causing an extremely hazardous spill. With a father and daughter in peril, Casey is forced to use extreme measures to remedy the situation. Dawson (Monica Raymund) and Brett (Kara Killmer) respond to an elderly woman who has a difficult senior advocate. Meanwhile, Mouch (Christian Stolte) and Brett continue along with their secret project together and Otis (Yuri Sardarov) shares some exciting news as he prepares himself for an unusual expedition.

Lt. Casey (Jesse Spencer) is unable to rescue a woman who becomes trapped inside her burning greystone, prompting him and Lt. Severide (Taylor Kinney) to butt heads over the husband's role in the tragedy. Herrmann (David Eigenberg) is on a mission to catch a mystery tagger that keeps targeting their firehouse and Boden gets a surprise visitor. Meanwhile, Dawson (Monica Raymund) and Brett (Kara Killmer) respond to a 16 year old boy who was injured during a romantic homecoming proposal.

While responding to a call in the field, Dawson (Monica Raymund) accidentally hits a pedestrian who stepped in front of the ambulance, and is left to deal with the repercussions. Lt. Casey (Jesse Spencer) and Lt. Severide (Taylor Kinney) disagree and continue to investigate an arson case while Chief Boden (Eamonn Walker) is left to decide whether to attend an important function in New York. Elsewhere, in hopes of preparing him for a possible promotion, Lt. Casey (Jesse Spencer) puts Herrmann (David Eigenberg) at the helm for a shift so he can discover firsthand what his superiors deal with.

It's a family reunion when Dawson (Monica Raymund) and Antonio's (guest star Jon Seda) mother and father come to Chicago for their big anniversary party, but things quickly turn south. When a deep secret comes to the surface involving his stepson James (guest star Juan Lozada), Chief Boden (Eamonn Walker) decides to take matters into his own hands. Meanwhile, Casey (Jesse Spencer) tries to save a young boy during a harrowing call to a warehouse and Otis (Joe Minoso) and Kidd (Miranda Rae Mayo) become competitive at the mud hundred race.

Lt. Casey (Jesse Spencer) and Dawson (Monica Raymund) apply for permanent adoption of Louie, but quickly discover a hurdle. Firefighter turned medical student Jeff Clarke (guests star Jeff Hephner) approaches Lt. Severide (Taylor Kinney) with an interesting proposition. With hopes of reinvigorating business at the bar, Otis convinces a skeptical Herrmann to throw a bash in celebration of the milestone 100th anniversary of Molly's, but not without complications.

Dawson (Monica Raymund) and Casey (Jesse Spencer) deal with legal matters in hopes of remaining Louie's legal guardians. Severide (Taylor Kinney) continues in his efforts for a bone marrow procedure to help Anna (guest star Charlotte Sullivan), but when things don't go as planned, he finds himself slipping back into old habits. Meanwhile, Brett (Kara Killmer) opens up to Dawson and members of Firehouse 51 become competitive, much to the dismay of Chief Boden (Eamonn Walker).

Severide (Taylor Kinney) agrees to a bone marrow donation but a work accident throws everything into flux. Casey (Jesse Spencer) and Dawson (Monica Raymund) try to find harmony at home. Meanwhile, Otis (Yuri Sardarov) and Mouch (Christian Stolte) decide to film a PSA encouraging people to join the Chicago Fire Department but hit a creative wall in the process.

Dawson (Monica Raymund) finds it hard to keep her emotions in check during an ambo run involving a pregnant teen. Elsewhere, the firehouse is called to the site of a building fire and Casey (Jesse Spencer) is forced to make a split second decision when two victims are each need of life saving assistance. In the aftermath, Casey is left to deal with the repercussions. Meanwhile, Severide (Taylor Kinney) shares a bond with Anna (guest star Charlotte Sullivan), as she makes her recovery.

The team is on high alert when a previous incident during a fire call leaves a dangerous man on the loose with a vendetta to target Lt. Casey (Jesse Spencer) and Firehouse 51, and prompts CPD to step in. Dennis Mack (guest star Nick Boraine), a buddy firefighter of Severide's (Taylor Kinney) father, comes to town to shadow the squad but may have ulterior motives. Meanwhile, Brett (Kara Killmer) and Antonio's (guest star Jon Seda) relationship hits some bumps in the road when his ex-wife Laura (guest star America Olivo) surfaces and Casey has a present for Dawson (Monica Raymund).

When truck and squad are summoned to the scene of a dangerous accident, Chief Boden (Eamonn Walker) makes a split second decision that overrides Chief Anderson (guest star Michael Hanrahan), the incident commander whose house was the first to respond to the call. Feeling his authority was undercut and his reputation damaged, Anderson uses his power to make things miserable for Boden and all of House 51 feels the repercussions. Meanwhile, Severide (Taylor Kinney) contemplates a major life changing decision, Herrmann (David Eigenberg) does a good deed and Brett (Kara Killmer) looks to make some personal changes to herself.

After exercising his disdain and authority over Chief Boden (Eamonn Walker), Chief Anderson (guest star Michael Hanrahan) reassigns members of 51 to various houses around town, citing the need for improvement. The ramifications are felt by the crew, who are left to make the best of their respective situations in their new surroundings. Boden fights to repair the situation, but it just might be out of his control. Elsewhere, Severide (Taylor Kinney) toils over an important decision.

Truck and squad are called to aid in a massive all city response when an old, ill equipped factory turned live/work space quickly turns into a firestorm, trapping countless unsuspecting victims. The dire situation quickly turns personal when it is discovered that one of Chicago PD's own has a family member at the scene. With the rescued victims in need of serious medical attention, the doctors and nurses of Chicago Med are tested as the major influx of patients are brought through their doors. Meanwhile, in the aftermath, the building owner steps forward to cooperate with the ongoing investigation, but the situation takes a sudden and unexpected turn.

When a turf war escalates, members of truck and squad find themselves caught in the middle as unsuspecting hostages when a group of armed gang members take cover and assume control over Firehouse 51. The situation turns even more dire when one of the infiltrators is wounded and in need of serious help.

When similar car accidents uncover the fact that someone may be targeting innocent people, a determined Dawson (Monica Raymund) takes matters into her own hands to help push things along. Severide (Taylor Kinney) does everything he can to make Anna (guest star Charlotte Sullivan) feel welcome in her new Chicago surroundings. Herrmann (David Eigenberg), Kidd (Miranda Rae Mayo) and Dawson decide to have Molly's included as a stop in this year's pub crawl, despite strong concerns from Otis (Yuri Sardarov), who may have his own reasons for standing alone. Meanwhile, Casey (Jesse Spencer) tends to his Alderman's duties when a persistent constituent asks for his help in resolving an issue.

Casey (Jesse Spencer) discovers a new crack house on the block that is harboring a female junkie and goes to extreme measures to remedy the situation. Dawson (Monica Raymund) and Brett (Kara Killmer) get assigned a new trainee (guest star Will Kiley) for the shift and the newbie gets the two in trouble when he surprises them during a harrowing call. Meanwhile, Severide (Taylor Kinney) gets an unexpected visit from his father, Benny (Treat Williams), and Herrmann (David Eigenberg) deals with family issues when his son Lee Henry (guest star David VonKampen) gets into trouble at school.

When the squad's rig breaks down in the field, Casey (Jesse Spencer) reunites with his old friend and colleague Jason Kannell (guest star Kamal Angelo Bolden) from Squad 6, whose crew gets assigned a temporary change of quarters until the rig issue is resolved. Dawson (Monica Raymund) and Brett (Kara Killmer) serve their time in retraining, both tackling the class in unique ways. Severide (Taylor Kinney) tries to remedy what is going on with Anna (Charlotte Sullivan) and finds support from unlikely sources. As Connie (DuShon Monique Brown) returns from her family engagement, the crew lays bets on how long her temporary replacement Marcy (guest star Mia Hulen) will last.

Casey (Jesse Spencer) goes to drastic measures to help his friend Kannell (guest star Kamal Angelo Bolden). Lt. Severide (Taylor Kinney) helps an old widow come to terms with letting go, but realizes he may be the one needing help. Otis (Yuri Sadarov) and Cruz (Joe Minoso) deal with surprises when they find a new roommate to move in. Dawson (Monica Raymund) and Brett (Kara Killmer) get crafty to save a young girl.

Cruz (Joe Minoso) finds himself in a bad spot when an off duty incident begins to unravel, prompting Mouch (Christian Stolte) to step in and offer help in hopes of avoiding serious consequences from the CFD. Casey (Jesse Spencer) goes head to head with a big politician to get his measure for first responders passed. Lt. Severide (Taylor Kinney) makes life difficult for newest team member Jason Kannell (guest star Kamal Angelo Bolden) and Dawson (Monica Raymund) gets an unexpected visit from her father (guest star Daniel Zacapa).

A dangerous warehouse fire puts truck and squad at risk. Tensions are high for Dawson (Monica Raymund) and Casey (Jesse Spencer) when Dawson's father (guest star Daniel Zacapa) overstays his welcome at their home. Meanwhile, Casey continues to fight for his first responders bill, Mouch (Christian Stolte) makes a serious decision regarding his future and Herrmann (David Eigenberg) goes to tremendous lengths to make a young boy smile.

Prepare for Season 5 of Chicago Fire with a look at the stunning cliffhanger that brought Season 4 to a close.

Lt. Casey (Jesse Spencer), who is at the center of an undercover operation to bring down a trafficking ring run out of Nesbitt's (guest star Eric Mabius) strip club, finds himself in very dangerous territory. Meanwhile, as a result of the high turnover rate on squad, Severide (Taylor Kinney) gets a rude awakening when Capt. Dallas Patterson (guest star Brian White) is brought in, much to Boden's (Eamonn Walker) dismay. Dawson (Monica Raymund) confirms her suspicions that her life is about to change forever and Jimmy Borrelli (guest star Steven R. McQueen), the new candidate, makes an unusual first impression. Elsewhere, citizens of Chicago band together to take charge of their neighborhood in protest of a drug den in their area, resulting in ramifications that severely hinder members of Firehouse 51, who are called to the scene to battle a blazing fire.

Members of the firehouse are frustrated with their inability to help Chief Boden (Eamonn Walker), whose job is on the line pending an internal investigation in the aftermath of a complicated call to a fire. Meanwhile, Lt. Severide (Taylor Kinney) struggles to accept his smaller role and adjusts to the presence of Capt. Patterson (guest star Brian White), his new commanding officer. Dawson (Monica Raymund) shakes things up on the work front and Casey (Jesse Spencer) attempts to find a crucial piece of evidence in his ongoing investigation against Nesbitt (guest star Eric Mabius). Elsewhere, Herrmann (David Eigenberg) struggles to keep the peace with Molly's newest neighbors.

The pressure on Firehouse 51 is at an all-time high as the internal affairs investigation into the handling of a recent fire picks up steam. Just when it appears that game-changing evidence comes to light that would serve to bail out Chief Boden (Eamonn Walker), new twists emerge that put his head right back on the chopping block. Brett (Kara Killmer) and Chili (Dora Madison) respond to a routine call and quickly find themselves in a life and death situation to help aid a stabbing victim who is bleeding out. Meanwhile, a stuck elevator summons the house to a high-rise hotel that tests everyone's mettle and candidate Jimmy Borrelli (guest star Steven R. McQueen) is conflicted when his older brother Danny (guest star Andy Ahrens) looks to get him transferred to a different house. Jesse Spencer, Taylor Kinney, Monica Raymund, David Eigenberg, Yuri Sardarov, Joe Minoso and Christian Stolte also star. Nick Gehlfuss, Oliver Platt, Brian Geraghty, Brian White, Rachel Nichols and Fredric Lehne also guest star.

One of 51's own needs the support of the entire house to recover from a near disaster. Meanwhile, Herrmann (David Eigenberg) has to figure out a way to reopen Molly's after it gets shut down and Severide (Taylor Kinney) digs deeper into the arson investigation, while struggling to cope with one of his toughest days yet. Jesse Spencer, Eamonn Walker, Monica Raymund, Kara Killmer, Dora Madison, Yuri Sardarov, Joe Minoso and Christian Stolte also star. Nick Gehlfuss, Jon Seda, Steven R. McQueen, Brian White and Rachel Nichols guest star.

After a fire ruins a neighborhood wedding, Boden (Eamonn Walker) steps up to host the ceremony at the firehouse. That's much to the chagrin of his boss, Chief Riddle (guest star Fredric Lehne), whose political aspirations have caused friction from within the firehouse. Meanwhile, Dawson (Monica Raymund), who returns to the house, also butts heads with Riddle over her ability to perform and is forced to defend herself despite Boden's support. Severide (Taylor Kinney) finds himself fighting for his way back to his old position and Capt. Patterson (guest star Brian White) is caught between loyalty towards leadership and loyalty to his colleagues.

Chief Boden (Eamonn Walker) meets his new neighbor (guest star Ilfenesh Hadera), who asks him for a favor that leads to serious consequences. Severide (Taylor Kinney) takes offense to being treated like a candidate by Captain Patterson (guest star Brian White) by undermining him during a call, and the situation reaches a boiling point. Cruz (Joe Minoso) receives a surprise visit from his past when Freddie (guest star Ralph Rodriguez), a gangbanger who knows Cruz's brother Leon, comes to visit and ask for a favor. Elsewhere, the team is called to a harrowing scene of an 18-wheeler and receive a thanks in the form of tickets to see the band Rush, much to Mouch (Christian Stolte) and Herrmann's (David Eigenberg) delight.

Chief Boden (Eamonn Walker) finds himself in the middle of a fiasco concerning a female neighbor (guest star Ilfenesh Hadera), who he believes is setting him up. Severide (Taylor Kinney), who is still on probation from his altercation with Captain Patterson (guest star Brian While), receives a surprise visit from his father (guest star Treat Williams) and discovers some interesting information on Patterson that could be a game changer. Meanwhile, romance blossoms at the Chicago Fire Department gala.

Chief Boden (Eamonn Walker) confronts Maddox (guest star Mark Hengst), believing he is the hand behind Serena's (guest star Ilfenesh Hadera) accusations intended to skew Boden's credibility from the approaching trial. Severide (Taylor Kinney) reaches out to Jamie (guest star Rachel Nichols), Maddox's lawyer, in an effort to help out and Capt. Patterson (guest star Brian White) questions Boden's ability to remain Chief. Meanwhile, Brett (Kara Killmer) and Chili (Dora Madison) discover a man passed out in a garden that may have a connection to a call from a previous crash site and Otis looks to fill up his social calendar, but the situation hits a bump in the road.

Members of Firehouse 51 are less than thrilled when Captain Patterson (guest star Brian White) steps in as replacement for Chief Boden (Eamonn Walker) while he deals with clearing his good name. When Severide (Taylor Kinney) learns of the potential whereabouts of Serena (guest star Ilfenesh Hadera), Chicago P.D's Officer Atwater (LaRoyce Hawkins) and Officer Ruzek (Patrick John Flueger) head to Lake Carlyle to try and uncover additional clues on Boden's case. Meanwhile, Herrmann (David Eigenberg) and Otis (Yuri Sardarov) give Freddie (guest star Ralph Rodriguez) a job that keeps him close by and Jimmy (Steven R. McQueen) and Chili (Dora Madison) elicit more attention then either bargained for, causing some friction between them.

The Firehouse is shocked to discover that one of their own becomes the surprising victim of a stabbing, and an attempted suicide raises some questions - a three-part story arc crosses over into "Chicago Med" and concludes the following night on "Chicago P.D." Members of Firehouse 51 band together and anxiously await word at Chicago Med when one of their own falls victim to a life-threatening stabbing. Cruz (Joe Minoso) urgently works with members of Chicago P.D. to track down Freddie's (Ralph Rodriguez) whereabouts when he goes missing. Dr. Choi (guest star Brian Tee) and Dr. Halstead (guest star Nick Gehlfuss) tend to an attempted suicide victim whose condition raises some eyebrows. Meanwhile, Mouch (Christian Stolte) surprises Trudy, (guest star Amy Morton) and Chili's (Dora Madison) odd behavior has Brett (Kara Killmer) and Jimmy (Steven R. McQueen) worried.

A tornado threatens the city and Herrmann (David Eigenberg) discovers the path may hit close to home. Chili (Dora Madison) and Brett (Kara Killmer) lock heads when Chili makes a critical mistake that leaves a victim breathless, prompting Brett to report to Chief Boden (Eamonn Walker) regarding Chili's erratic behavior. Meanwhile, Otis (Yuri Sardarov) pleads for Dawson (Monica Raymund) to help him solve his women troubles, and Severide (Taylor Kinney) is asked to lend assistance to agent Alex Ward (guest star Liza Bennett) from the Department of Homeland Security regarding a suspicious home.

Herrmann (David Eigenberg) goes to court to testify against Freddie (guest star Ralph Rodriguez), but when the perpetrator's father (guest star Ski Carr) reaches out to beg forgiveness for his son's malicious attack, a tormented Herrmann is left to figure out what to do. Following the aftermath of the recent tornado, Lt. Casey (Jesse Spencer) learns the makeshift shelter housing victims is on the brink of shutting down. At the request of Alderman Colin Becks (guest star Armand Schultz), Casey attends a fundraiser and is thrown into the spotlight, only to quickly discover that his good intentions might not have the impact he was hoping for. Dawson (Monica Raymund) and Brett (Kara Killmer) feel the repercussions after telling Boden (Eamonn Walker) about Chili's (Dora Madison) recent erratic behavior. Meanwhile, Severide (Taylor Kinney) helps Agent Alex Ward (guest star Liza Bennett) solve a homemade explosives case, and Otis (Yuri Sardarov) receives a welcome surprise.

The firehouse is on high alert when mysterious threats begin to emerge throughout Chicago. The situation turns dire when news of a mass shooting brings members of squad and truck into the middle of a dangerous and harrowing scene. Lt. Casey (Jesse Spencer) works diligently to investigate the missing money from the fundraiser for the victims of the recent tornado. Meanwhile, Jimmy (Steven R. McQueen) agrees to represent the firehouse in the first annual "Battle of the Badges" boxing match against the 21st district police department, and Chili's (Dora Madison) erratic behavior continues to be a major issue for her ambulance partner, Brett (Kara Killmer).

Lt. Severide (Taylor Kinney) confronts Chili (Dora Madison) about his suspicions regarding her erratic behavior, but she does not take too kindly to his intentions. Meanwhile, members of the firehouse rally around Lt. Casey (Jesse Spencer), who they believe is a perfect candidate to run for the position as Alderman, and Jimmy (Steven R. McQueen) faces off against Antonio (Jon Seda) in the first annual "Battle of the Badges" boxing match.

Firehouse 51 responds to an odd call from a neighboring firehouse and the unusual circumstances prompt Severide (Taylor Kinney) and Cruz (Joe Minoso) to take the investigation into their own hands to search out the real story. The truck welcomes new firefighter Stella Kidd (guest star Miranda Rae Mayo), but her addition has repercussion inside the firehouse. Meanwhile, Casey (Jesse Spencer) moves forward in his run for alderman, but begins to realize that some voters have their own personal agendas for wanting him elected.

Casey (Jesse Spencer) continues his run for alderman, but a citywide propaganda attack against his campaign makes him reconsider his candidacy. The rescue squad is summoned to the scene of a man trapped inside of a burning car with suspicious evidence suggesting that the fire may have been intentionally set. Mouch's (Christian Stolte) upcoming bachelor party looms, but with Trudy's (guest star Amy Morton) nerdy brother Larry (guest star Zack Pearlman) handling the details, everyone fears for the worst. Meanwhile, Jimmy (Steven R. McQueen) and Brett (Kara Killmer) take a kidnapping investigation into their own hands.

While responding to a potential carbon monoxide leak inside a home, Lt. Severide (Taylor Kinney) and Cruz (Joe Minoso) uncover the remains of a child inside the chimney. Subsequent information leads Severide to believe that the discovery may be linked to a case he had worked on years ago. Meanwhile, with election day nearing, Casey (Jesse Spencer) braces for the worst in his run for Alderman, prompting Dawson (Monica Raymund) to enlist the firehouse team to lend a hand to the cause. Complicating his chances, Alderman Becks (guest star Armand Schultz) continues to bad mouth Casey to the press, but an incident in the field might prove beneficial.

While responding to a call involving a victim incapacitated with a leg wound, Sylvie Brett (Kara Killmer) witnesses a murder and is threatened by the shooter not to go to the police. Unsure of what to do, she tries to track down Antonio (guest star Jon Seda) from Chicago PD. Elsewhere, Firehouse 51 jumps into action when a fire breaks out inside a restaurant, trapping several people inside a fault. Meanwhile, with his wedding day to Trudy (guest star Amy Morton) fast approaching, a nervous Mouch (Christian Stolte) starts to get cold feet.

When a high school student becomes an innocent victim of a gang retribution incident, a very determined Lt. Casey (Jesse Spencer) tries all means necessary to resolve the issue. Severide (Taylor Kinney) lends a hand to Detective Holloway (guest star Jenny Mollen), who is working a dangerous undercover investigation, and watches over her 9yearold son at the firehouse. Brett (Kara Killmer) and Jimmie (Steven R. McQueen) are called to aid a woman who takes a fond liking to Jimmy. Meanwhile, Otis (Yuri Sardarov) makes a surprising discovery that leaves him very concerned and Herrmann (David Eigenberg) goes toetotoe with Stella (guest star Miranda Rae Mayo) to claim bragging rights over who can best run a bar.

Detective Holloway (guest star Jenny Mollen) continues to entrust Lt. Severide (Taylor Kinney) to watch over her young son at the firehouse while she testifies in court as part of an undercover operation. When the situation takes an unexpected turn, Severide is left to deal with the aftermath. The firehouse responds to a blaze at an art gallery that has a victim trapped inside and prompts Cruz (Joe Minoso) to make a rash decision amid the chaos. Casey (Jesse Spencer) receives a suspicious package in the mail that casts suspicion on him from the Board of Ethics. Meanwhile, Brett (Kara Killmer) discovers Otis (Yuri Sardarov) isn't taking care of his own important issues and confronts him, but finds he is stubborn and more interested in rallying the troops to organize a trip to Las Vegas for the annual firefighting conference.

Dawson (Monica Raymund) makes an attachment to a young boy she rescues in an apartment blaze while Kidd's (guest star Miranda Rae Mayo) big idea for Molly's turns into a disaster. Lt. Severide (Taylor Kinney) makes a pitch for the house to upgrade some of their fire masks but hits a wall in his efforts, prompting Lt. Casey (Jesse Spencer) to use his political influence to pull a few strings. Meanwhile, Cruz (Joe Minoso) and a reluctant Brett (Kara Killmer) bring in a secret weapon in their efforts to get Otis (Yuri Sardarov) to see Dr. Halstead (guest star Nick Gehlfuss) and take a blood test.

Truck and squad are called to the scene of a building collapse that has trapped more than a dozen victims inside of the rubble. With the structure ready to give way and not much time to react, Chief Boden (Eamonn Walker) faces a difficult decision with lifeanddeath ramifications. In her quest to foster Louie, Dawson (Monica Raymund) throws all her energies into the bureaucratic process necessary to make it happen, but it is the helping hand of a familiar face that gives her a fighting chance. Currently on medical leave, Otis (Yuri Sardarov) swings by the firehouse and meets his temporary replacement, hoping it is just that but fearing the worst. Meanwhile, Severide (Taylor Kinney) and Kidd (guest star Miranda Rae Mayo) continue to see each other outside of the firehouse, and Casey (Jesse Spencer) and Antonio (guest star Jon Seda) find themselves at odds and tensions flare.

Lt. Boden (Eamonn Walker) and Jimmy (Steven R. McQueen) find themselves at odds in dealing with the aftermath of recent events while Kidd (guest star Miranda Rae Mayo) is forced to deal with her unstable and volatile ex, Grant (guest star Guy Burnet). With the help of firehouse 51, Dawson (Monica Raymund) tries to put her best foot forward in her pursuit for fostering Louie. At the urging of Susan Weller (guest star Lauren Stamile), his new political consultant, Casey (Jesse Spencer) tends to his Alderman duties and leaves town with her to attend a three-day summit. Much to his surprise, Casey embraces his new role while Susan urges him to consider grander aspirations. Meanwhile, the house responds to a dangerous structure fire that puts one of their own in a desperate situation.

Before diving into Season 4, see how Season 3 ended in shocking fashion - as a personal discovery leads Dawson to a major shock.

Boden (Eamonn Walker) forces members of Firehouse 51 to pull themselves back together in the aftermath of a harrowing fire explosion. When Severide (Taylor Kinney) goes missing for one week too many, Casey (Jesse Spencer) works to track down his whereabouts. Meanwhile, Newhouse (Edwin Hodge) brings some unexpected news regarding one of Mills' (Charlie Barnett) relatives while Herrmann (David Eigenberg) and Otis (Yuri Sardarov) make some new goals regarding Molly's.

Lieutenant Severide (Taylor Kinney) returns to Firehouse 51, but he is clearly not his usual self and Dawson (Monica Raymund) counts down the weeks until she gets started as a candidate at the Austin Firehouse. Meanwhile, Mills (Charlie Barnett) learns more about his father's family and Herrmann (David Eigenberg) asks the rest of the Molly investors to come up with some new ideas to turn the business around.

Fingers get pointed and tempers flare between members of Firehouse 51 and the Austin firehouse when fire trucks collide en route to a perilous call. Meanwhile, Boden (Eamonn Walker) has a plan to get Dawson (Monica Raymund) her badge, but it comes at a cost. Elsewhere, Mills (Charlie Barnett) confronts his past and his future on the same day and the Molly's crew hits some hurdles starting up their new food truck.

Dawson (Monica Raymund) starts her first day as a candidate and looks to find a balance with Lieutenant Casey (Jesse Spencer) inside the firehouse. Mills (Charlie Barnett) must come to terms with a future that doesn't include the squad. Meanwhile, Severide (Taylor Kinney) confronts his demons in an unexpected way and the Molly's crew has a date with the city inspector to make sure their food truck is up to code.

Lieutenant Casey (Jesse Spencer) deals with the fallout of his sister Christie's (guest star Nicole Forester) impending divorce. Meanwhile, Dawson (Monica Raymund) and Mills (Charlie Barnett) settle into their new roles at Station 51. Elsewhere, Brett (Kara Kilmer) can't decide if she wants to leave Chicago and the Molly's crew still can't figure out how to get the food truck started.

Casey (Jesse Spencer) comes to the aid of his sister Christie (guest star Nicole Forester) and faces down his corrupt brother-in-law; while Brett (Kara Killmer) goes above and beyond for a mother in need. Elsewhere; Mills (Charlie Barnett) gets educated on the exciting world of unlicensed private investigation and Dawson (Monica Raymond) begins training with Herrmann (David Eigenberg). Taylor Kinney; Eamonn Walker; Yuri Sardarov; Joe Minoso and Christian Stolte star. Randy Flagler and Edwin Hodge guest star.

Members of Firehouse 51 are forced to contend with a house fire, but when the injured owner is rescued from his cellar clutching a suspicious box, Lt. Severide (Taylor Kinney) brings in Sergeant Voight (guest star Jason Beghe, Chicago P.D.) and Detective Lindsay (guest star Sophia Bush, Chicago P.D.) into the mix for further investigating. Elsewhere, Mills (Charlie Barnett) wonders if the dangers of Newhouses's (guest star Edwin Hodge) off-duty gig are worth the cash returns, while Molly's II is in dire need of a good chef.

When a massive helicopter explosion in a densely populated area leaves a trail of debris scattered across a full city block, members of the firehouse spring into action as lives hang in the balance. Squad 3 finds itself in a precarious position, Brett (Kara Killmer) is cornered by a dangerous man in the midst of the madness and Dawson (Monica Raymund) is shocked to discover what actually brought the chopper down.

When the team responds to a semi-truck leaking hydrochloric acid in a busy intersection, Casey (Jesse Spencer) and Dawson (Monica Raymund) find their relationship being put to the test. Meanwhile, Severide (Taylor Kinney) learns more about Brittany's (guest star Serinda Swan) past and Mouch (Christian Stolte) has some difficulties in his dating life.

A house fire leads members of the truck and squad to race to save the lives of the couple trapped inside, and then are faced with the perplexing aftermath. Meanwhile, Chief Boden (Eamonn Walker) prepares to start his new family, while the combination of life at work and home pushes Casey (Jesse Spencer) and Dawson (Monica Raymund) apart. Elsewhere Molly's II has its chance to shine at the Chicago Holiday Fest.

Two firehouse members are abducted, triggering a desperate search by the Chicago P.D. Elsewhere, Casey and Dawson struggle to balance their personal and professional lives, and Chief Boden deals with news that his newborn has potential complications.

Severide (Taylor Kinney) and Dawson (Monica Raymund) discover startling evidence found at a storage unit fire that appears connected to the fire that took Shay's life. Meanwhile, the firehouse bands together when Chaplain Orlovsky (guest star Gordon Clapp) is the victim of a bad car accident. Elsewhere, Chief Boden's (Eamonn Walker) father (guest star Richard Roundtree) visits, but quickly wears out his welcome with his unsolicited parenting advice.

More clues surface surrounding the fire that killed Shay, leading Severide (Taylor Kinney) to a most unexpected source who may be able to provide pertinent information. Meanwhile, Shay's sister Megan (guest star Ellen Woglom) comes to town, prompting members of the firehouse to remember Shay's life. Elsewhere, Cruz (Joe Minoso) is in for a surprise when Otis's (Yuri Sardarov) grandmother moves into their apartment, while Boden finds a way to help his dying father (guest star Richard Roundtree) make the most of his last few weeks.

Mills (Charlie Barnett) and Brett (Kara Kilmer) race to recover a missing teenager and are left stranded in the unforgiving elements, while the rest of Firehouse 51 babysits an abandoned newborn. Meanwhile, Lt. Severide (Taylor Kinney) receives an interesting job proposal and Chief Boden (Eamonn Walker) finds himself at odds with his father (guest star Richard Roundtree) over his treatment and the planning of a big party in his honor.

Interim Chief Pat Pridgen (guest star Matthew Del Negro) is brought over to temporarily fill in for Boden (Eamonn Walker), who is left to tend to his personal affairs. When tension is sparked as the result of his derisive leadership, the absence of Chief Boden (Eamonn Walker) becomes all too apparent. Meanwhile, Lieutenant Severide (Taylor Kinney) must deal with a most unwelcome addition to his squad, Brett (Kara Killmer) gets closer to a girl she previously rescued and Casey (Jesse Spencer) starts seeing a new woman, Beth (guest star Bree Williamson), but interesting complications quickly unfold.

Chief Pridgen (guest star Matthew Del Negro) comes under fire after making a tactical error during an apartment fire for which he throws Lt. Casey (Jessie Spencer) under the bus, leading Lt. Severide (Taylor Kinney) to take it upon himself to clear the problem. In an effort to further cover himself from any wrongdoing, Pridgen enlists the help of Lt. Welch (guest star Kenny Johnson), who is faced with the choice of whether to fit in with the firehouse or follow his superiors self-serving orders. Elsewhere, Mouch (Christian Stolte) is floored upon learning that his donation to a fertility clinic has resulted in a child who, now a young adult, wants to meet him. Meanwhile, Brett (Kara Killmer) and a reluctant Cruz (Joe Minoso) take Dawson (Monica Raymund) out on a double date and Boden (Eamonn Walker) focuses his efforts on his duties at home as a father.

Lt. Severide (Taylor Kinney) lobbies Chief Boden (Eamonn Walker) for a favor for Scott Rice (guest star Warren Christie), an old friend needing a second chance with the CFD, but Casey (Jesse Spencer) and Otis (Yuri Sardarov) have their doubts. Elsewhere, Mills (Charlie Barnett) works to regain his active squad status while Brett (Kara Killmer) and Dawson (Monica Raymund) decide they need a big night out.

During a harrowing call to a structure fire, Herrmann (David Eigenberg) rescues a trapped toddler, but the questionable circumstances surrounding the event sends him on a personal mission to locate the father and get to the bottom of the situation. Severide (Taylor Kinney) makes up for lost time by retracing key friendships from his adolescence, while Mills (Charlie Barnett) discovers some surprising news. Elsewhere, Cruz (Joe Minoso) and Brett's (Kara Killmer) relationship comes to a crucial juncture, while Otis (Yuri Sardarov) develops some unexpected feelings.

It's all hands on deck when Firehouse 51 races to the scene of a deadly chemical leak inside an industrial building. With squad and truck tested like never before, scores of workers are rescued but many are experiencing respiratory distress. This prompts truck 81, squad 3 and ambulance 61 to spring into action to transport the victims to nearby Chicago Med. The situation takes a turn from bad to worse in the midst of the chaos when a "patient" planted inside the hospital goes on a suicide mission armed with a grenade and claiming to be the carrier of a deadly airborne disease. Trying to stop the madman from engaging the explosive device, a member of the firehouse team is severely wounded in the blast and left to face life-threatening injuries. With no other choice, Chicago Med is forced into lockdown until doctors and the Hazmat team can determine the severity of the airborne virus.

Truck and squad are called to the scene of a car crash that has Mills (Charlie Barnett) desperately working to save the life of a driver seriously injured in the wreck. Meanwhile, Casey (Jesse Spencer) has some doubts about Jack Nesbitt (guest star Eric Mabius), whose strip club he is remodeling on the side. Elsewhere, Hermann (David Eigenberg), Otis (Yuri Sardarov), Cruz (Joe Minoso) and Chaplain Orlovsky (guest star Gordon Clapp) help get their team ready for the peewee hockey championship, but Herrmann might prove more of an obstacle than the other team.

An apartment fire linked to a case of rape and attempted murder calls for members of the CPD to team with the Special Victims Unit, which had a similar unresolved case that has eluded them for more than 10 years. This prompts Sgt. Benson (Mariska Hargitay) to come in from New York to assist with the investigation in which she is all too familiar. Meanwhile, doubts among the squad towards one of their own causes Severide (Taylor Kinney) to lay down the law and Dawson (Monica Raymund) puts her life on the line during a call.

At Sgt. Voight's (guest star Jason Beghe) urging, a determined Lt. Casey (Jesse Spencer) agrees to go undercover in an effort to provide proof of Jack Nesbitt's (guest star Eric Mabius) shady dealings. Meanwhile, Otis (Yuri Sardarov) and Severide (Taylor Kinney) continue to disagree about the integrity of Scott Rice (guest star Warren Christie), causing tensions to flare between members of truck and squad. Meanwhile, Herrmann (David Eigneberg) helps out a fellow member of the firehouse.

Lt. Casey (Jesse Spencer) puts his life on the line and digs deeper into the shady dealings of Jack Nesbitt (guest star Eric Mabius). With members of truck and squad at odds over Rice's (guest star Warren Christie) actions in the field, Chief Boden (Eamonn Walker) is left to figure out how to create unity in a divided house, while Severide (Taylor Kinney) comes to question his own judgment. A dangerous warehouse blaze quickly gets out of control and threatens members of firehouse 51, prompting Boden and Cruz (Joe Minoso) to risk everything to save their own. Elsewhere, Dawson (Monica Raymund) gets some life-changing news.

The actress behind Rebecca Jones describes filming her first fire experience.

Guest star Edwin Hodge chats about joining the 51 team and overcoming fears .

Evidence recovered at a series of fires indicates that Lt. Severide (Taylor Kinney) is being targeted by an arsonist. Meanwhile, Battalion Chief Boden (Eamonn Walker) clashes with Gail McLeod (guest star Michelle Forbes), a high ranking consultant with the State Marshal's office who keeps a sharp eye on budgets and performance at the city's firehouses - and has 51 under her microscope as one that could face the prospect of being closed. Elsewhere, Lt. Casey (Jesse Spencer) reflects on the year anniversary of Andy's death, Shay (Lauren German) has suspicions about Severide's paternity and Mouch (Christian Stolte) enjoys a visit from Mari (guest star Cindy Chang), his Japanese girlfriend.

In the wake of Heather's (guest star Chaon Cross) incident, Lt. Casey (Jesse Spencer) is having a hard time handling his newfound responsibilities. Lt. Severide (Taylor Kinney) is on edge dreading the next attack from the firehouse's arsonist. Meanwhile, with Renee (guest star Sarah Shahi) back from her mother's, Severide knows he has to confront her about his paternity suspicions. Elsewhere, Mouch (Christian Stolte) begins his campaign for union president and Shay (Lauren German) and Dawson (Monica Raymund) feel that they need to get out more.

Lt. Severide (Taylor Kinney) has his strong ideas on who the serial arsonist is, but first needs to find proof to back up his suspicions. Meanwhile, Lt. Casey (Jesse Spencer) adjusts to his new lifestyle in the wake of recent events and Molly's bar is failing, much to the dismay of owners Hermann (David Eigenberg), Dawson (Monica Raymund) and Otis (Yuri Sardarov). Elsewhere, Dawson goes out on a date with Jay Halstead (guest star Jesse Lee Soffer), one of the bar regulars, and Mouch's (Christian Stolte) campaign trail starts to get on track with the aid of Isabella (guest star Mena Suvari), an old friend of Dawson's.

Lieutenant Severide (Taylor Kinney) is anxious to implicate the serial arsonist, while Dawson (Monica Raymund) and Shay (Lauren German) get a shock on a routine call. Meanwhile, suspicions continue to point to Clarke (guest star Jeff Hephner) as the mole inside the firehouse and Molly's falls deeper into the red. Elsewhere, Mouch (Christian Stolte) campaigns for union president, with the aid of Isabella (guest star Mena Suvari), and Boden (Eamonn Walker) butts heads with Gail McLeod (guest star Michelle Forbes).

Boden's (Eamonn Walker) future with Firehouse 51 is on the line and McLeod (guest star Michelle Forbes) keeps on him about his past wrongdoings, pushing him toward an early retirement. With Boden considering his options, McLeod calls on an unlikely candidate to potentially replace him as Chief. Meanwhile, it becomes clearer who the mole inside the firehouse is and everyone takes measures to make their disdain for him known. Meanwhile, Shay's (Lauren German) social life is in full bloom and Arthur (guest star Mike Starr) continues to take money from the struggling Molly's.

While out on a jog, Severide (Taylor Kinney) comes across a secluded and empty construction site and encounters a young boy who has been trapped in a backhoe loader and is in dire need of assistance. Boden (Eamonn Walker) and McLeod (Michelle Forbes) continue to butt heads about the future of the firehouse and Boden breaks news about his future to Casey (Jesse Spencer). Meanwhile, it's election day for the union presidency and Mouch (Christian Stolte) and Greg Sullivan (guest star Eric Slater) have a debate on Otis' (Yuri Sardarov) podcast. With rival bar Game Day's future in peril, the finger is being pointed at Molly's.

When a tanker collides into a commuter train that subsequently crashes into a warehouse, the firehouse is called to the horrific scene that tests everyone to the limits as life and death hangs in the balance. With the ultimatum in place for him or the firehouse, Boden (Eamonn Walker) is tasked with making life-changing decisions regarding his future. Severide (Taylor Kinney) learns more about Katie (guest star Brittany Curran), the young woman he saw with his father (guest star Treat Williams). Meanwhile, Shay (Lauren German) and Dawson (Monica Raymund) are still at odds and Casey's (Jesse Spencer) responsibility of being a surrogate father takes a sharp turn.

When the shooting of a young girl happens in their neighborhood, Cruz (Joe Minoso) and his brother, Leon (guest star Jeff Lima) are forced to think about the gang they have tried to escape. The battle between Chief Boden (Eamonn Walker) and McLeod (guest star Michelle Forbes) continues to escalate and Isabella (guest star Mena Suvari) convinces Mills (Charlie Barnett) to dress up for a fancy gala. Meanwhile, Lt. Casey (Jesse Spencer) is sad Dawson (Monica Raymund) won't be coming by as much now that his parental duties are over, Shay (Lauren German) is fed up with the firehouse and digs in deeper with Devon (guest star Vedette Lim) and Zoya's (guest star Larisa Polonsky) visa is expiring, prompting her to come up with an idea.

Battalion Chief Boden (Eamonn Walker) prepares to counterattack McLeod (guest star Michelle Forbes) in a final effort to save the firehouse from closure and the romance between Dawson (Monica Raymund) and Casey (Jesse Spencer) escalates. Leon (guest star Jeff Lima) is making progress in the gang murder investigation, but Cruz (Joe Minoso) cannot stand being left in the dark by Voight (guest star Jason Beghe), fearing for his brother's safety. Meanwhile, Severide (Taylor Kinney) and Katie (guest star Brittany Curran) bond to make up for lost time and Otis (Yuri Sardarov) feels uncomfortable living with Severide and Shay (Lauren German) after Devon's (guest star Vedette Lim) latest escapade.

All seems lost with firehouse 51 on the verge of closing its' doors, thanks in no small part to Gail McLeod (guest star Michelle Forbes), but Chief Boden (Eamonn Walker) and the rest of the house refuse to allow themselves to sit by and let it happen. An emergency call to an apartment structure fire tests everyone's limits and puts the squad in harm's way. Meanwhile, Dawson (Monica Raymund) receives some life-changing news and union president Greg Sullivan (guest star Eric Slater) makes headlines, which has an immediate impact on Mouch (Christian Stolte).

Lt. Casey (Jesse Spencer) returns to work at Firehouse 51 after nearly being killed in a building collapse and Shay (Lauren German) meets Allison Rafferty (guest star Christine Evangelista), her new partner, who is friendly to everyone except her. Dawson (Monica Raymund) begins her rigorous training at the Chicago Fire Academy, while Lt. Severide (Taylor Kinney) prepares for his stint as instructor. Meanwhile, Clarke (guest star Jeff Hephner) stubbornly does not speak with the police about the murder in which he is the prime suspect and the future of Molly's looks bleaker than ever.

Lieutenant Casey (Jesse Spencer) tries to convince himself and everyone around him that he is one hundred percent healthy following his near-death incident in the line of duty. Shay (Lauren German), not wanting to delve into the emotionally traumatic incident, continues to elude a lawyer who wants to speak with her about Daryl's suicide. Meanwhile, Otis (Yuri Sardarov) and Katie (guest star Brittany Curran) bond over board games, Boden (Eamonn Walker) helps out a woman (guest star Melissa Ponzio) with a negligent landlord and Dawson (Monica Raymund) notices fellow recruit Rebecca Jones (guest star Daisy Betts) undertaking some interesting test-taking techniques at the Academy.

When a drunk driver knocks down a transformer, the entire neighborhood is left without power on a frigid Chicago night and members of Firehouse 51 step up to lend their much needed help. While many from the community ride out the night at the station, in the midst of such close quarters, romances speed up and tempers flare. Meanwhile, Casey (Jesse Spencer) continues to lie to both himself and Dawson (Monica Raymund) about his condition and the stakeholders in Molly's bicker about the bar's direction.

Severide (Taylor Kinney) feels sidelined as he leaves Detective Lindsay (guest star Sophia Bush) and the Intelligence Unit to do their job and locate his sister Katie (guest star Brittany Curran). Shay (Lauren German) gets an unusual tip from Chicago Blackhawk players Brent Seabrook and Duncan Keith, who makes friends with Clarke (guest star Jeff Hephner) and stop by Molly's. Meanwhile, Casey (Jesse Spencer) learns more about his head injuries after another close call and Dawson (Monica Raymund) pushes hard to pass the physical test at the Academy.

Severide (Taylor Kinney) is getting impatient with the police as Vince Keeler (guest star Jake Weary) walks free. Meanwhile, the house pulls out all the stops to save a girl trapped inside a donation bin, Mouch (Christian Stolte) learns that Boden's (Eamonn Walker) secretary Connie (gust star DuShon Brown) is not someone to mess with and the squad and truck are called to a serious high rise fire inside a 20-story downtown office building.

Lt. Severide (Taylor Kinney) hits the top of the list as Det. Lindsay (guest star Sophia Bush) starts calling in suspects with the clearest motives to make the guy who kidnapped Katie disappear. Meanwhile, Jones (guest star Daisy Betts) is still having trouble fitting in as word of her disruptions reach the fire department's headquarters. Elsewhere, Herrmann (David Eigenberg) celebrates his twentieth anniversary with his wife, but no one supports his idea on the gift he intends to give.

Lt. Severide (Taylor Kinney) is reminded of his own past by a man he saves from a car accident (guest star W. Earl Brown) and feels compelled to help him. Elsewhere, Lt. Casey (Jesse Spencer) and Chief Boden (Eamonn Walker) grapple with how to dock Jones (guest star Daisy Betts) per her father's orders. Meanwhile, Mouch (Christian Stolte) and Dawson (Monica Raymund) have troubles with the opposite sex and an emotional call to duty creates ripples throughout Firehouse 51.

Lt. Severide (Taylor Kinney) sticks his neck out for Dave Bloom (guest star W. Earl Brown), a fellow firefighter from Denver who is troubled by addiction. Elsewhere, Dawson (Monica Raymund) and Shay (Lauren German) leave town for a "girl's weekend" at a cabin in the woods. Meanwhile Jones (guest star Daisy Betts) struggles with the knowledge that her father is pressuring Chief Boden (Eamonn Walker) about her career path and Mouch's (Christian Stolte) internet dating profile gets an upgrade with the help of Mills (Charlie Barnett) and the guys.

A suicide note is delivered to a surprised Dawson (Monica Raymund) and Lt. Severide (Taylor Kinney) digs deeper into Bloom's (guest star W. Earl Brown) dark past. Elsewhere, Chief Boden (Eamonn Walker) learns shocking news, and with the help of Shay (Lauren German), Lt. Casey (Jesse Spencer) goes on the search for a life-changing item.

Lt. Casey (Jesse Spencer) and Dawson (Monica Raymund) volunteer to help at a charity run at Chicago Medical when a massive explosion sends Chicago into chaos. With one of their own missing in the blast, the firehouse is tested like never before.

With everyone's support, Dawson (Monica Raymund) makes final preparations to retake the fireman's exam, but a call to the field may throw a major wrench into her plans. Elsewhere, Lt. Casey (Jesse Spencer) has an important matter to discuss with Antonio (guest star Jon Seda, "Chicago P.D."). Meanwhile, Lt. Severide (Taylor Kinney) and the firehouse welcome Rick Newhouse (guest star Edwin Hodge), the latest addition to the squad, Shay (Lauren German) gets an uninvited surprise guest and Chief Boden (Eamonn Walker) makes a bold move.

A fire at a boarding school leaves Lt. Severide (Taylor Kinney) shaken and wondering if he could have done more. Meanwhile, with the firehouse in full support of Dawson (Monica Raymund) as she retakes the fireman's exam, Lt. Casey (Jesse Spencer) attempts some political maneuverings on her behalf. Elsewhere, Mills (Charlie Barnett) looks for answers about his father's mysterious past and Chief Boden's (Eamonn Walker) grand plans take a detour.

A compilation of the show's steamiest moments so far.

Features Monica Raymond's Dawson, who must put her training and confidence to the test when she is alone in the station during an emergency.

For the firefighters, rescue squad and paramedics of Chicago Firehouse 51, no occupation is more stressful or dangerous, yet so rewarding and exhilarating.

Severide is hiding a serious shoulder injury sustained in the fire that killed Andy Darden, and grapples with his guilt as he fights to rescue a construction worker trapped in a building collapse. Adding to the burden, Darden's wife Heather turns on Severide at the annual firefighters' barbecue, blaming him for her husband's death. A call is made to an accident site at Hancock Tower, where two teenagers are pinned in a vehicle trapped beneath the falling debris of a broken window washer's cart. Meanwhile, Casey and Hallie work to figure out their future together.

When the drunk driver who hits a car and paralyzes a 16-year-old boy turns out to be the son of a dirty cop, Lieutenant Casey must decide whether or not to turn him in. Facing pressure and subsequent threats from the powerful and well-connected Detective Voight, Casey decides to tell the truth, inviting a stand-off. Additionally, Severide, who's fighting off the advances of the Chief's new assistant, learns he has a fractured vertebra in his neck that may never heal if he doesn't get treated, but ignores the doctor's advice so he can continue working. Meanwhile, Mills is torn between helping his mother at her restaurant and devoting himself full-time to the fire department, like his father did.

Chief Boden (Eamonn Walker) is accused of leaving a homeless man to die in a warehouse fire after ordering his men to evacuate the scene, creating negative press and bad feeling within the department. Meanwhile, Lieutenant Severide (Taylor Kinney) helps an elderly woman facing some neighborhood problems. Detective Voight (guest star Jason Beghe) ramps up his intimidation tactics aimed at Casey (Jesse Spencer) in an attempt to discourage him from testifying against his son. Shay (Lauren German) is forced to revisit her heartbreak over her ex-girlfriend Clarice (guest star Shiri Appleby), when she finds herself face-to-face with the ex and her husband during a call. Hermann's (David Eigenberg) temper flares during a rescue call at a Halloween block party. Monica Raymund, Charlie Barnett and Teri Reeves also star.

Casey confronts Detective Voight about his harassing tactics, vowing never to back down, and ends up paying the price for his decision. Dawson faces disciplinary action for her on-the-job conduct. Meanwhile, Severide finds his arm failing him during a rescue at a construction accident, and reaches out to Anna, an old flame and pharmaceutical rep, hoping she might be able to help alleviate his injury problems.

Facing suspension, Dawson gets a hand from the same girl she saved through the procedures that landed her in front of the disciplinary board. Lieutenant Casey finds his fuse shortening as Detective Voight stops at nothing to get him to retract his statement. However, when Casey lays his life on the line during an apartment fire, he may have unknowingly caught the break he was needing.

Everyone in the firehouse is ordered to take a drug test after a call to a daycare center exposes them to a makeshift meth lab, and Severide stalls, not wanting his injury, or the painkillers he takes, to be discovered. Meanwhile, Truck and Squad find themselves pinned down by gunfire while trying to help the victim of a gang shooting, and a deep-fried turkey fire grows from small to explosive when a garage catches fire. Elsewhere, Dawson saves a bleeding man and Casey delivers a baby on the scene of a massive car pileup on the freeway.

At the site of a train accident, Peter Mills (Charlie Barnett) becomes deeply upset when he observes the dead body of a young victim. Unable to shake his emotional distress about the event, he questions his future as a firefighter. Dawson (Monica Raymund) and Shay (Lauren German) save a 6-year-old girl whose mother (guest star Kat McDonnell) is abusing her -- but their confrontation leads the woman to resort to dire actions. Meanwhile, Severide (Taylor Kinney) aggravates his injury while rescuing a heart attack victim and Shay sends Clarice (guest star Sheri Appleby), her married, pregnant ex-girlfriend, back home to her husband. Jesse Spencer, David Eigenberg and Eamonn Walker also star.

After he's injured in a terrible fire at an auto machine shop, Jose Vargas is forced to go on disability and leave his life as a firefighter behind - a task he finds incredibly difficult. Chief Boden tries to help a suspected teenage firebug. Also, Severide receives an enticing invitation from Renee, a woman who he saved from a car crash incident involving live electrical wires. Meanwhile, Cruz tries to save his younger brother Leon from the gang he is involved with.

After putting out a kitchen fire in an upscale townhouse, Casey, Herrmann, Mouch, Cruz, Otis and Mills find themselves accused of stealing a $50,000 diamond necklace from the home, touching off an internal investigation. Cruz's brother Leon is caught in the middle of an escalating gang war, leaving Cruz to make a desperate choice to save him. Meanwhile, Dawson invites Casey to her cousin's fancy Christmas party, and a frustrated Shayhas reached her limit with Severide.

Eaten up by his guilt over Flaco's death in the fire, Cruz goes to Casey to confess. While Shay recovers from a head injury sustained in the ambulance crash, Severide asks Dawson for her help in dealing with his own injury. Casey is caught in the middle of a family conflict between his mother and sister. Elsewhere, Herrmann finds a business deal hard to stomach.

Severide (Taylor Kinney) finally addresses Chief Boden (Eamonn Walker) about his injury and makes some important personal decisions about his future. Meanwhile, Casey (Jesse Spencer) struggles with family matters and Dawson (Monica Raymund) takes matters into her own hands when she discovers a young girl who is the sole survivor at the scene of a rescue call. Lauren German, Charlie Barnett and David Eigenberg also star. Sarah Shahi, Kathleen Quinlan and Nicole Forester guest star.

A troubled Chief Boden goes to the police when a man dies in a hardware store fire set by Ernie, the troubled teenage firebug he's been trying to help, and his Uncle Ray. Meanwhile, Severide decides on his future and reaches out to his father. Elsewhere, Otis finds camaraderie when he fills in for a few shifts at the slowest firehouse in the city, and makes a decision of his own, while Dawson and Shay find themselves in a bad predicament during a call to a tenement apartment.

Severide (Taylor Kinney) finds that he shares a familiar past with Eric Whaley (guest star Shane McRae), the Lieutenant who was brought into the firehouse to help out. Dawson (Monica Raymund) lets Shay (Lauren German) in on her secret, while Casey (Jesse Spencer) deals with family issues. Meanwhile, a bad batch of heroin on the streets has Boden (Eamonn Walker) and the team scrambling, while Clarice (guest star Shiri Appleby) and Shay find they have a new problem to overcome. Charlie Barnett and David Eigenberg also star. Kathleen Quinlan and Jon Seda also guest star.

Dawson attempts to help her brother Antonio unravel the details of his drugs-and-gang investigation, and goes behind his back in turning to an unlikely source for assistance. Casey and his mother, Nancy struggle with their new relationship. Meanwhile, as a favor to Lieutenant Whaley (guest star Shane McRae), Severide visits someone important from his past, while Herrmann and Otis learn some hard truths about their "silent partner" in the bar.

The anguish that haunts Cruz over his previous actions boils over, as he puts himself and his fellow firefighters in jeopardy. Casey and his sister Christie try to solve their issues with their mother and each other. Meanwhile, Severide reaches out again to an important person from his past as a favor to Lieutenant Whaley and the squad gains new perspective after assisting the bomb squad on an extremely dangerous call.

Old emotional wounds are opened when Lieutenant Severide's father Bennie comes to town and clashes with Chief Boden over the death of their former colleague. Mills helps a distraught driver who caused an accident and Shay makes a decision about her future with Clarice. Meanwhile, Herrmann, Otis and Dawson get to the bottom of a mystery about their bar.

With tensions still running high between Chief Boden (Eamonn Walker) and Bennie Severide (guest star Treat Williams), things boil over when Mills confronts Bennie about the fire that killed his father. Meanwhile, Severide (Taylor Kinney), Casey (Jesse Spencer) and Bennie uncover the truth behind two mysterious diner fires and Shay (Lauren German) takes a new direction with her plan to have a baby. Monica Raymund, Charlie Barnett and David Eigenberg also star. Chaon Cross guest stars.

Tragedy strikes when a rescue attempt at a tenement building proves unsuccessful, leaving the men and women of firehouse 51 affected by the loss of the victim. Severide's (Taylor Kinney) decision to put Mills (Charlie Barnett) on the fast track to move from Truck to Squad doesn't sit well with some of the others and tension mounts between Severide and Casey (Jesse Spencer) over Heather Darden (guest star Chaon Cross). Shay (Lauren German), and Dawson (Monica Raymund) are forced to deal with a junkie's crazy behavior while on a call and Shea considers a different way to have a family. Meanwhile, the team draws the ire of local drug dealers who threaten the peace and safety of the neighborhood and firehouse.

Mills (Charlie Barnett) finds himself the target of resentment from some colleagues when Severide (Taylor Kinney) supports his desire to join Squad. Tara (guest star Brooke Nevin), a paramedic candidate, joins Dawson (Monica Raymund) and Shay (Lauren German) on the job for a few shifts. Meanwhile, Shay comes to the aid of Cindy Herrmann (guest star Robyn Coffin), who suffers from pregnancy complications while her husband Christopher (David Eigenberg) is out of town. Elsewhere, Dawson and Casey (Jesse Spencer) draw closer as the grand opening of Molly's draws near, and Casey receives a surprise visit.

Detective Voight (guest star Jason Beghe) returns, looking to collect on the favor that Dawson (Monica Raymund) owes him for helping her brother, Antonio (guest star Jon Seda). Casey (Jesse Spencer) falls back into old patterns in his personal life, while Dawson, Herrmann (David Eigenberg) and Otis (Yuri Sadarov) become the proud owners of a real neighborhood bar as Molly's prepares for its grand opening. Meanwhile, Severide's (Taylor Kinney) career is threatened.

A frustrated Severide (Taylor Kinney) turns to an unlikely ally to resolve his current dilemma. Casey (Jesse Spencer) begins to find satisfaction in his personal life, while Mills (Charlie Barnett) and Dawson (Monica Raymund) face personal challenges. Meanwhile, the squad is called to the scene of a harrowing apartment building collapse.

Events force Lieutenant Casey (Jesse Spencer) to team up with the Intelligence Unit, now run by Voight (guest star Jason Beghe), who doesn't appear to have changed his crooked ways after his stint in prison. Shay's (Lauren German) excitement at the prospect of becoming a parent grows, while Mills (Charlie Barnett) and Dawson (Monica Raymund) face some personal challenges. Meanwhile, the house comes together to support the opening of Molly's.

When a call comes in from the Cook County jail, the squad steps into a volatile predicament and are tasked with trying to defuse an escalating situation. Shay (Lauren German) remains hopeful about her baby dreams and Hermann's (David Eigenberg) wife Cindy (guest star Robyn Coffin) goes into labor with their fifth child. Meanwhile, Mills (Charlie Barnett) and Dawson (Monica Raymund) face key decisions in their personal lives. Taylor Kinney, Jesse Spencer and Eamonn Walker also star.