Halstead's partying with Camila unintentionally puts him in the middle of a drug-related homicide. He's forced to choose between loyalty to his unit and his girl. Meanwhile, Voight finally discovers the mole in his unit.

Halstead and Atwater go under cover to prevent military-grade weapons from hitting the street; Voight calls in a favor to clear Olinsky's name for Bingham's murder.

Intelligence suspects the leader of a local mosque is behind the bombing of an Army recruitment station. After a second explosion, Voight urges Halstead to follow the facts and not let his time in the service cloud his judgment.

With the threat of a gang war looming, Voight and Ray Price must organize a peace summit to end the bloodshed before more innocent people get hurt. Burgess evaluates her future with Blair.

When Upton and Ruzek answer an emergency call to an abandoned house, their investigation leads them down a dark path.

The team investigates a string of brutal pharmacy robberies, and Halstead connects with one of the victims about their Army careers. Upton suspects there is more to the story and confides in Voight.

Torres finds himself in the midst of a murder case that hits close to home and threatens to expose his troubled past. As he struggles to reconcile his old life with his new one, Voight keeps a watchful eye.

Ruzek grapples with his father's worsening condition while Intelligence searches for an elusive serial killer.