Casey reconsiders his run for alderman after he's targeted by a propaganda campaign. The squad responds when a man is trapped inside of a burning car. Trudy's nerdy brother plans Mouch's bachelor party. Jimmy and Brett investigate a kidnapping on their own.

While responding to a call in the field, Dawson accidentally hits a pedestrian who stepped in front of the ambulance, and is left to deal with the repercussions. Lt. Casey and Lt. Severide disagree and continue to investigate an arson case while Chief Boden is left to decide whether to attend an important function in New York. Elsewhere, in hopes of preparing him for a possible promotion, Lt. Casey puts Herrmann at the helm for a shift so he can discover firsthand what his superiors deal with.

It's a family reunion when Dawson and Antonio's mother and father come to Chicago for their big anniversary party, but things quickly turn south. When a deep secret comes to the surface involving his stepson James, Chief Boden decides to take matters into his own hands. Meanwhile, Casey tries to save a young boy during a harrowing call to a warehouse and Otis and Kidd become competitive at the mud-hundred race.

Dawson and Casey deal with legal matters in hopes of remaining Louie's legal guardians. Severide continues in his efforts for a bone marrow procedure to help Anna, but when things don't go as planned, he finds himself slipping back into old habits. Meanwhile, Brett opens up to Dawson and members of Firehouse 51 become competitive, much to the dismay of Chief Boden.

The crossover continues on Chicago P.D. S04E09 Don't Bury This Case (II).

Truck and squad are called to aid in a massive all-city response when an old, ill-equipped factory-turned live/work space quickly turns into a firestorm, trapping countless unsuspecting victims. The dire situation quickly turns personal when it is discovered that one of Chicago PD's own has a family member at the scene.

The crossover continues on Chicago P.D. S04E016 Emotional Proximity (II) and Chicago Justice S01E01 Fake (III).

When a turf war escalates, members of truck and squad find themselves caught in the middle as unsuspecting hostages when a group of armed gang members take cover and assume control over Firehouse 51.

Brett attempts to make a lifesaving decision in the field to someone near and dear to the firehouse family. In an effort to impress Lily, Otis scrambles to get everything together for the grand opening of Molly's North. Meanwhile, Boden becomes emotional following the rescue of a famous blues player from a burning apartment building and Dawson struggles to come to terms with how she has been dealing with her father.

Halloween is in full effect for Foster and Brett, who are summoned to a home where a prank has quickly turned serious. Gorsch continues his reign of terror on Firehouse 51.

A rare but deadly bacteria takes its toll on numerous victims around the city, leaving Chicago’s finest first responders to work together alongside the CDC to resolve the dangerous situation. Following a fire at a local university that ties into the outbreak, Severide has suspicions that something bigger is happening.

The crossover continues on Chicago Med S05E04 Infection, Part II (II) and Chicago P.D. S07S04 Infection, Part III (III).