as Detective Alvin Olinsky: A seasoned undercover veteran and Voight’s right-hand man.

The season finale involves a massive manhunt for the escaped cartel leader Pulpo and a shocking betrayal within the unit.

as Sergeant Hank Voight: The intense, often ethically-grey leader of the Intelligence Unit.

The season balances high-stakes criminal investigations with the personal dramas of the squad: Key Plot Points

A gun-smuggling case involves high-caliber rounds; Halstead faces a ghost from his past.

as Detective Sheldon Jin: The unit's tech and surveillance expert.

as Trudy Platt: The sarcastic, no-nonsense desk sergeant (recurring in Season 1, later a main cast member). Episode Guide Summary

as Officer Adam Ruzek: A rookie recruited straight from the academy by Olinsky.