While chasing a heroin supplier, CPD crosses paths with a convicted criminal recently released on a technicality. Halstead's history with the man threatens the team's ability to put him back in prison.

A murder in a Bulgarian neighborhood results in a challenging investigation when locals won't talk to police. Ruzek has a clash with a patrol officer.

Voight pulls Darius in after Crawford asks Intelligence to investigate a dangerous drug, but there is little trust in the relationship. When their plan to nail a dealer goes awry and another CI is murdered, the team must make a tough decision about Darius.

Voight and the team pursue a ruthless crime ring whose business has hit close to home. As they dig deeper, the extent of the danger becomes more apparent. Deputy Superintendent Samantha Miller second-guesses her decisions.

When a P.D. informant is murdered, the team digs in to track down the perpetrator only to learn a shocking truth. Voight and Ruzek strategize to help Burgess.

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.

When a family is poisoned in their home, the team discovers a connection to the Becks. Ruzek goes undercover to work for their business, and as he gets closer to Samantha, chilling information about her father, Richard, comes to light.