Firehouse 51 must band together after a devastating fire catches them off guard. Vasquez continues his quest for answers. Violet and Novak face an unexpected roadblock in the new training protocol.

A dangerous warehouse fire puts truck and squad at risk. Tensions are high for Dawson and Casey when Dawson's father overstays his welcome at their home. Meanwhile, Casey continues to fight for his first responders bill, Mouch makes a serious decision regarding his future and Herrmann goes to tremendous lengths to make a young boy smile.

Truck and Squad clash after a tense call rescuing a doomsday prepper. Herrmann struggles with Cindy's diagnosis. Violet gives Brett and Gallo dating advice.

A new face at Firehouse 51 causes tension, while rising chaos in the city brings new challenges to the team. Herrmann stalls on plans of relinquishing his office to Mouch.

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).

Casey goes to drastic measures to help his friend Kannell. Lt. Severide helps an old widow come to terms with letting go, but realizes he may be the one needing help. Otis and Cruz deal with surprises when they find a new roommate to move in. Dawson and Brett get crafty to save a young girl.

The mattress factory fire spirals out of control. Truck and squad lay it on the line in hopes of getting the trapped victims out alive.

The Chicago fire team works seamlessly with Chicago Med personnel to help aid victims of a deadly gas leak, but things quickly take a turn for the worse when the hospital is suddenly forced into quarantine.

The team responds to a mass shooting; Casey investigates the missing money from the fund-raiser. Jimmy agrees to represent the firehouse in a boxing match against the Chicago PD's 21st District. Chili's behavior continues to be an issue for Brett.

Firehouse 51 unites to help a young boy in tragic circumstances. A high-powered political consultant helps Casey navigate a potential scandal. Cruz makes a mistake that nearly costs him his life.

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.

Tragedy strikes when a rescue attempt at a tenement building proves unsuccessful, leaving the men and women of firehouse 51 affected by the loss of the victim. Severide's decision to put Mills on the fast track to move from Truck to Squad doesn't sit well with some of the others and tension mounts between Severide and Casey over Heather Darden. Shay and Dawson are forced to deal with a junkie's crazy behavior while on a call and Shay considers a different way to have a family. Meanwhile, the team draws the ire of local drug dealers who threaten the peace and safety of the neighborhood and firehouse.

The members of the firehouse spring into action when a helicopter explodes over a populated area.

Lt. Casey puts his life on the line and digs deeper into the shady dealings of Jack Nesbitt. Chief Boden must figure out how to create unity in a divided house, while Severide comes to question his own judgment. A dangerous warehouse blaze quickly gets out of control and threatens members of firehouse 51.

Lt. Casey finds himself in a bad spot when a forklift accidentally pierces a tank storing acid. Casey is forced to use extreme measures to help a father and daughter in peril. Dawson and Brett respond to an elderly woman who has a difficult senior advocate. Mouch and Brett continue with their secret project. Otis shares some exciting news as he prepares himself for an unusual expedition.

After exercising his disdain and authority over Chief Boden, Chief Anderson reassigns members of 51 to various houses around town, citing the need for improvement. The ramifications are felt by the crew, who are left to make the best of their respective situations in their new surroundings.

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).

Mouch builds a classic firetruck model for the Deputy District Chief but needs some assistance from Gallo and Ritter. Brett and Violet encounter multiple victims with a strange set of symptoms. Cindy's chemotherapy results loom over the Herrmann family.

Brett waits for life-changing news. Herrmann encounters a psychic with a grave warning on a call. Kidd finds a new lead on the Homeland Security case.

A frustrated Severide, turns to an unlikely ally to resolve his current dilemma. Casey begins to find satisfaction in his personal life, while Mills and Dawson face personal challenges. Meanwhile, the squad is called to the scene of a harrowing apartment building collapse.

Lt. Casey and Dawson volunteer to help at a charity run at Chicago Medical when a massive explosion sends Chicago into chaos. With one of their own missing in the blast, the firehouse is tested like never before. The crossover continues on Chicago P.D. S01E12 8:30 PM (II)

Tensions run high when trucks from two firehouses collide and fingers are pointed towards Cruz for his driving.

The squad members come together to support one of their own. Herrmann tries to figure out how to reopen Molly's after it gets shut down. Severide digs deep into the arson investigation.

Patterson fills in for Boden, who's trying to clear his name. Severide learns where Serena may be hiding. Herrmann and Otis give Freddie a job that keeps him close by. Jimmy and Chili draw more attention then either bargained for.

Casey and Dawson find themselves in the midst a potential political mess. Stella has to make a big decision about her ex-beau. The squad responds to an auto accident. Severide befriends a socialite. Brett and Mouch set aside their writing differences for the greater good.