AC12 and the Major Violent Crime unit lock horns over the tragedy at the hospital and the evidence surrounding the ambush. Meanwhile Kate (Vicky McClure) continues to work undercover with Lindsay (Keeley Hawes) in Missing Persons. They look into the disappearance of 15-year-old Carly Kirk, a case Lindsay appears personally invested in. She is secretive and volatile as the evidence against her mounts, but it's clear she won't go down without a fight. As Lindsay starts to scrutinize the background of the AC-12 officers, they're forced to go on the defensive - Kate, Steve (Martin Compston) and Hastings (Adrian Dunbar) all have reasons for wanting to keep their private lives under wraps. As public and private pressure on the case reaches frenzied levels, it appears that the team's conduct might compromise the case against Lindsay.