Atwater and Burgess are given a new patrol car, but are challenged with keeping it brand new. A run in with a psychotic woman leads the Intelligence Unit to discover a drug smuggling operation which has put several girl’s lives in peril. Voight’s overprotective act with Lindsay leads her right where he doesn’t want as she also helps to keep Justin out of trouble. Meanwhile on stakeout, things get tense between Olinsky and Ruzek as Olinski tries to teach him the finer points of surveillance.

Halstead's badge is revoked when Lonnie Rodiger is found dead; Severide and Clarke find Dr. Elliot's torso; Sumner tries to prove herself; Lindsay shares a moment with Severide.

As Antonio’s life is now in question, Voight and Platt open up about their pasts. Jin is caught while tinkering with Voight’s computer and uses the only scapegoat possible to keep him in the clear. At the same time with Charlie back in town Lindsay realizes she’s going to have to come clean about a few things. Halstead finally gets answers he’s been wanting about Voight’s and Olinsky’s past.

Intelligence begins to look into a string of murders where the victims have a dollar bill pinned to their chests. Thanks to some digging by Ruzek, Voight learns his friend was involved in some shady business dealings. Antonio and Halstead follow-up on some leads that help focus in on the culprit and motives for the murders. Burgess and Roman investigate a series of house break-ins and get some help from Desk Sgt. Platt.

A friend of Nadia’s leads the intelligence unit to a huge heroin bust. Unfortunately this bust results in Olinsky arriving home to find the suspects are holding his wife. Voight and the team think they’ve found a common thread with the suspects but it’s not who they think. Meanwhile Burgess and Roman are given an assignment where they get paired with a K-9 officer, Jenn Cassidy who is Roman’s former partner and girlfriend.

Bunny comes to Lindsay concerned about a suspicious repeat customer at her husband’s rental company. This lead brings Intelligence into a case which robbery-homicide has been working for months.

Led by Olinksy, Intelligence hunts down an elusive Chinatown gangster.

Retired Commander Perry enlists Voight and the team to help extract his cop nephew from a unit of corrupt officers who are robbing drug dealers. When things go bad Voight must take down a younger, more violent version of himself. Meanwhile, Lindsay struggles to stay clean. At the same time a woman from Olinsky's past reaches out to him.

A bust to bring down a heroin kingpin goes horribly awry. Olinsky reveals a dark secret from his past, and Halstead tries to get through to a spiraling Lindsay.

The team investigates a band of rogue operatives.

The discovery of a headless body in Lake Michigan points to Hank's mob connections. Roman risks everything to help a grieving mother.

Voight arranges for his former cellmate, Eddie Little, to be a CI in an effort to bring down a major cocaine supplier. Burgess makes a major move regarding her relationship with Ruzek. Roman develops a plan to help fund Platt and Mouch's wedding.

While out on a bank run for his off-duty security job at the dispensary, Halstead and his co-workers find themselves under attack by a violent robbery crew. Meanwhile Roman, Burgess, Antonio, Halstead, Ruzek and Atwater follow-up on a lead and track down a potential suspect.

In the Season 3 finale, the team investigates the murder of a single mom who was in contact with Voight's now-reformed son, who was himself brutally assaulted. Meanwhile, Roman makes a major decision and Crowley plans to make changes within the unit.

Intelligence investigates when a young man is beaten and his fiancée is apparently abducted. Lindsay surprises Halsted with a big question. Cdr. Fogel takes Platt to task for going over his head to have Tay assigned to District 21.

Severide is brought into the District for questioning after his car is found to have caused a deadly crash. As the investigation gets underway, the team works to uncover a group of car-jackers who may be the key to Severide's innocence.

The crossover starts on Chicago Fire S05E09 Some Make It, Some Don't (I).

When Lindsay is tipped off about a grieving father looking to avenge his daughter's death, Olinsky goes undercover as a hitman-for-hire. With Gang Intelligence lacking enough evidence to arrest the original gangbanger in question, the team works to reinvestigate the case. Meanwhile, Ruzek comes back after finishing his undercover assignment only to have Voight knock him down to patrol duty.

When the team is called to an in-progress bank robbery, they come across Detective Hailey Upton trying to take over the crime scene with her Robbery-Homicide unit - butting heads with Voight in the process. As the robberies continue to be executed around the city, Lindsay is forced to make a decision in the heat of the moment.