Hand-picked as the head of the unit is Voight, who has assembled a team of diverse detectives who share his passion and commitment to keep the city safe. They include Jay Halstead (Jesse Lee Soffer), a brash young detective who previously saw active military duty in Afghanistan; Officer Kim Burgess (Marina Squerciati), who has proven herself valuable to the team after being brought up from patrol on several past cases; Officer Adam Ruzek (Patrick John Flueger), a quick-witted cadet plucked from the police academy; Officer Kevin Atwater (LaRoyce Hawkins), a charismatic patrolman who was brought upstairs; and Det. Hailey Upton (Tracy Spiridakos), the newest member of the team with killer instincts, humor and smarts. After going head to head with Voight, the two find a mutual respect for one another and see the value in working together.

Desk Sgt. Trudy Platt (Amy Morton) runs a tight precinct with tough love, although she lets her softer more vulnerable side shine through from time to time.