When an assistant district attorney is killed, detectives first suspect a prostitute, but new evidence reveals it is someone closer to home.
After a series of brutal murders, Sergeant Hank Voight and District 21 go after a Colombian drug cartel cleaning house in Chicago, but complicated histories and unit rivalries begin to surface.
Casey must work with Voight and the Intelligence Unit; Shay grows increasingly excited about motherhood; the house come together to support the opening of Molly's.
Voight and the team take a look at a house that has been linked to a series of gangs; Halstead struggles to maintain his composure when he is confronted by people from his past.
Voight's new Internal Affairs handler begins questioning his actions, as Voight is forced to team up with his old partner from the Gang Unit.
