The Big Bang Theory

Leonard and Sheldon (series stars JOHNNY GALECKI and JIM PARSONS) are brilliant physicists – geniuses in the laboratory, but socially challenged everywhere else. Enter beautiful, street-smart neighbor, Penny (series star KALEY CUOCO-SWEETING), who aims to teach them a thing or two about life. Despite their on-again, off-again relationship in the past, Leonard and Penny have finally gotten engaged. Even Sheldon has found a female companion – entering into a “Relationship Agreement” with neurobiologist Amy Farrah Fowler (series star MAYIM BIALIK). In their free time, Leonard and Sheldon enjoy fantasy role-playing games with their ever-expanding universe of friends, including fellow scientists Raj (series star KUNAL NAYYAR) and Howard (series star SIMON HELBERG), and Howard's adorable microbiologist wife, Bernadette (series star MELISSA RAUCH).

When Sheldon is forced to teach a class, Howard surprises everyone by taking it. Meanwhile, the tension between Penny and Bernadette gives Amy a chance to play both sides. Guest star REGINA KING returns as Mrs. Davis, the University’s Director of Employee Relations.

Howard is nervous when NASA asks him to throw out the first pitch at a Los Angeles Angels game for National Space Day. Also, Leonard and Penny try to prove Sheldon wrong after he claims that he and Amy are a superior couple.

Raj’s honesty about his past comes back to bite him after his girlfriend is cold to Penny. Meanwhile, the guys consider becoming part-owners in Stuart’s comic-book store.

Amy and Bernadette accuse Penny of being a “buzzkill” after she gets an email from work during their Vegas weekend. Meanwhile, the guys try to invent something cool, but only come up with new ways to procrastinate.

Sheldon and Raj test whether they could survive a dark-matter research expedition in a salt mine by simulating the conditions in a steam tunnel deep underground. Meanwhile, Leonard and Penny seek advice from Wolowitz and Bernadette after they fight about money.

The guys try to help Penny out of an awkward work dilemma, when a smitten doctor shows up at her door after her flirtatious sales techniques work a little too well. Meanwhile, Amy and Bernadette argue over whether or not female scientists should play up their sexuality.

When the gang recreates a high-school prom night on the roof of the guys’ apartment building, Sheldon feels pressure to participate in all the typical romantic traditions.

When Leonard gets minor surgery on his nose, Sheldon is the one in need of sympathy. Meanwhile, Raj’s parents’ impending divorce causes Howard and Bernadette to work on their own marriage.

While Sheldon says a tearful goodbye to the final installment of “Fun with Flags,” Leonard, Howard and Raj search for something significant in a dead professor’s research. And Bernadette is shocked to learn of her co-workers’ true feelings from Penny.

Leonard and Howard turn to Raj for help in dealing with a work emergency when they nearly come to blows after blaming each other for a potential disaster at the university. Amy throws an authentic Victorian Christmas party, while Sheldon seeks revenge on her for making him celebrate the holidays

When the guys finally agree to do something the girls like, it leads to a confrontation between Leonard and Sheldon.

Sheldon worries his comfortable lifestyle is preventing him from achieving scientific progress so he asks his friends to make him miserable.

After Leonard and Sheldon co-publish a physics paper, they must defend themselves against criticism from an online bully. Also, girls’ night finds Penny, Amy and Bernadette confronting embarrassing moments from their pasts.

Howard receives some shocking news as everyone prepares for the reopening of Stuart’s comic book store. Penny teaches Sheldon how to “let it go” but can’t follow her own advice after she learns something infuriating about Amy. Also, Leonard and Raj think they spot Nathan Fillion at a restaurant.

When the gang hears about an experiment designed to make participants fall in love, Sheldon and Penny put it to the test as a joke. Meanwhile, Leonard, Amy, Raj and Emily spend the evening trying to escape a room with a “zombie.” And Bernadette and Howard run into trouble at the airport after returning from the funeral for Mrs. Wolowitz.

A trip to the pet store ends in a fight when Amy learns that Sheldon has applied for a one-way mission to colonize Mars. Also, Leonard surprises Penny with a very “adult” purchase; and Raj is caught snooping in Emily’s apartment.

Friction ensues when a magazine fails to mention Leonard in an article about the paper he co-wrote with Sheldon. And a blackout at Mrs. Wolowitz’s home leads to a final family dinner in her honor.

When Leonard and Sheldon are invited to speak at UC Berkeley, they take a detour to try to sneak on to George Lucas’s Skywalker Ranch to meet one of their idols. Back in Pasadena, Howard and Bernadette battle over the fate of his Dr. Who TARDIS, while Raj and Amy offer to settle the dispute with a game of ping pong.

When Sheldon and Amy build a blanket fort, they come to a big crossroads in their relationship. And Wolowitz is shocked when a man claiming to be his half-brother he never knew he had shows up at his front door. And, when Penny is invited to appear on Wil Wheaton’s podcast, she and Leonard have a huge, on-air argument.

When Raj is asked to create a message in case a NASA mission discovers alien life, the guys fight over what he should do. Meanwhile, Penny is torn between auditioning for a movie or keeping her successful pharmaceutical sales job.

Wolowitz questions his engineering abilities when he and Sheldon can’t get a drone to fly. Meanwhile, a canceled flight nearly prevents Leonard from giving the commencement address at his former high school. And Raj pits his parents against each other when his father cuts him off financially.

Personalities collide and sparks fly when Sheldon and Leonard’s mothers (special guest stars LAURIE METCALF and CHRISTINE BARANSKI) finally meet. Meanwhile, Howard decides to “man up” and do his fair share of the housework – but not without a little help from his friends.

In the eighth season finale, Sheldon presses Leonard and Penny to choose a date for their wedding, while dealing with dramatic changes in his own relationship with Amy.