After a series of deadly ambushes, the team goes under cover to bring down a dangerous new drug dealer who is determined to push out the competition; Ruzek's informant proves to be a loose cannon, which could upset the whole operation.

After a seemingly innocent young man is gunned down in the street, the team works to bring in the suspected culprit, but the case is more complex than it appears; the grief-stricken father is determined to do his own undercover work.

The team investigates a rash of car jackings and finds the truth is more complicated than it seems; Burgess makes a discovery about a previous case that will change her life forever.

A cop is murdered, and suspicion falls on someone who has been holding a grudge against the officer; intelligence works hard to solve the case, but Deputy Superintendent Samantha Miller is hesitant to defend him until she knows the whole story.

Ruzek and Burgess discover a child walking alone in the middle of the street, and when they take her home, they discover that her entire family has been murdered; Upton is approached with a job offer from the FBI.

When the son of an influential former officer is implicated in a murder, Moore pressures Voight to charge him quickly; the stakes are raised in Atwater's fight against the blue wall after patrol officers stop responding to his team's calls.

The team responds to the shooting of a 5-year-old girl and must work the case while facing the heightened attention on police reform; Atwater is targeted by officers who want to hurt him for standing against the blue wall.