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.

A child abduction case hits too close to home for Dawson. Lindsay and Bunny's relationship reaches a critical impasse and Roman reveals his secret to Burgess.

The team is terrorized by a gun-wielding father who is desperate to find his missing daughter. Bunny stirs up accusations of misconduct from Voight's past.

Voight seeks revenge on the man who tried to kill him. A rumor causes a rift in Intelligence.

Ruzek's job is on the line after an ill-fated undercover op.

The team investigates a band of rogue operatives.

The team investigates a Columbine-like threat at a private school. Atwater seeks out a mentor; Olinsky's marriage faces a crisis.

The team discovers the mutilated body of a government official while responding to an informant's tip about an upcoming drug trade. Meanwhile, Burgess helps plan a surprise for Platt.

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

Intelligence investigates a doctor who gave his patients lethal doses of chemotherapy. Roman fights a wrongful shooting investigation.

The crossover starts on Chicago Fire S04E10 The Beating Heart (I) and Chicago Med S01E05 Malignant (II).

Intelligence hunts down a crew responsible for a rape and robbery rampage. Lindsay is abducted on an undercover operation.

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.

Lindsay goes undercover to catch a rogue cop who targets women at casinos. Platt risks her life in a negotiation crisis.

While working at a sobriety checkpoint, Burgess finds a duffel bag full of heroin in the truck of a respected college professor who claims to know nothing about how the drugs ended up there. At District, Roman expresses his desires to become a Field Training Office to Platt, and Mouse sets Halstead up with an off-duty security job working for the attractive owner of a medical marijuana clinic.

When a young boy is executed, Intelligence turn to the boy's parents for information and upon further investigation, discover the father has a criminal background and was a part of a local gang.

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.

While responding to a call of shots fired, Voight, Antonio, Halstead and the team come across a secret battered woman's shelter and discover the owner has been wounded and a resident of the shelter has been kidnapped. Burgess and Roman go undercover to track down a man robbing people by catfishing them on a dating app. Lindsay opens up to Halstead about her past.

When Burgess and Lindsay respond to a call about a stabbing, the assailant turns out to be a kidnapping victim escaping her captor; Ruzek accuses Roman of having feelings for Burgess.

Responding to a call about a suspicious duffel bag at the Chicago Lakefront, Voight is horrified to discover that the bag contains the frigid and unmoving body of a newborn baby. Meanwhile, Voight is surprised to hear that his son is in town and Burgess and Roman grow closer.

Burgess gives chase after Roman is wounded by a hooded perp who opened fire on their patrol car and shoots who she thinks is the suspect, but no gun is found at the scene—and the person she shot is a 17-year-old honor student.

Lindsay and Halstead respond to a shots fired call and discover one survivor: a young girl. Antonio and Olinsky investigate a "self help" group. Platt makes the case to Crowley for why Burgess and Roman should remain partners.

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.