Voight employs his new informant to help solve a tricky drug trafficking case; Atwater, who once again struggles to reconcile his personal and professional life, reaches a decision.
The team works together to identify the head of the brutal Los Temidos gang; Voight dives deeper into his informant Anna Avalos' past when her undercover role is threatened.
As the team closes in on drug kingpin Javier Escano, Voight is forced to lie to his undercover informant Anna to keep her on track; their deteriorating trust threatens an increasingly tenuous operation.
As the team works to bring down a drug ring, Voight builds trust with a new informant; however, it soon becomes clear she has a plan of her own.
Halstead takes a new recruit under his wing during an investigation; the dynamics are challenging, however, and questions arise over the recruit's complicated past.