The officers of 15 Division are forced to release a suspected predator for lack of evidence. But when Dov and Chris make a grim discovery -- a missing girl's body, hidden in a deserted ravine -- all bets are off. Detective Luke Callaghan returns to oversee the homicide investigation, and soon realizes this might be the work of a serial killer. When they learn that Andy has been assaulted and Gail violently abducted following the call girl sting, the officers rally in a race against time to track down Gail's captor before it's too late. Following up on a simple lead, one officer ends up directly in the path of the killer. Will it end with the ultimate sacrifice?

When a death threat aimed at a local priest leads Andy and Nick to a neighborhood drug lord, the officers realize that they're navigating a delicate war zone and that the priest may be hiding some surprising secrets of his own. Meanwhile, Gail and Traci pick up one of the drug runners - a young girl whose refusal to be an informant compels Traci to make a major decision about her career. Chris and Swarek clash over what it takes to make a good cop, and Dov's new relationship takes a dramatic and dangerous turn.