Season 4 featured several "One Chicago" crossovers that connected the unit to Chicago Fire and Chicago Med :
In a devastating multi-episode arc, Alvin Olinsky (Elias Koteas) loses his daughter, Lexi, in a warehouse fire, pushing him to a grief-stricken breaking point.
In the season finale, Lindsay resigns from the Chicago Police Department to accept a position with the FBI in New York after being investigated for her conduct during an assault on a suspect. Off-screen, Bush cited abusive behavior and harsh working conditions as her reasons for leaving. Chicago P.D. - Season 4
Part of a massive three-way crossover with Fire and Justice centering on the warehouse fire that killed Olinsky’s daughter.
In "All Cylinders Firing," Desk Sergeant Trudy Platt (Amy Morton) is brutally attacked outside her father's home, leading to a personal and harrowing investigation into her past. Season 4 featured several "One Chicago" crossovers that
's fourth season is a pivotal chapter that fundamentally altered the series' trajectory through major cast departures and a shift toward more topical story arcs. Airing from September 2016 to May 2017, the season consists of 23 episodes focused on the professional and personal fallout of Sgt. Hank Voight's (Jason Beghe) vigilante actions. 🎬 Key Character Departures and Arrivals
Midway through the season (Episode 8), Antonio leaves the Intelligence Unit to join the State’s Attorney’s office as a chief investigator, a move designed to lead into the spin-off Chicago Justice . Part of a massive three-way crossover with Fire
Briefly joined the unit as a recurring detective while Adam Ruzek (Patrick John Flueger) was on an undercover assignment. Major Plot Arcs