Firehouse 51 hosts a Halloween open house. Kidd and Severide help a young girl after she gets kicked out of her home.

Following an injury in the aftermath of an industrial fire, Severide and Seager work together to investigate an anonymous tip. Kidd searches for the right person to fill the opening on Truck 81.

Kidd and Severide's honeymoon is interrupted by a dangerous person from their past. Kidd's former academy classmate joins Firehouse 51. Brett and Violet reflect on their relationships.

A new chief shakes things up at Firehouse 51. Violet and Novak work to uncover the truth behind a car crash. Cruz keeps a watchful eye on Severide and Damon's growing bond.

After a daring rescue at an adventure park, Kidd asks Severide to create a ropes course for Girls on Fire. Violet’s former nemesis returns, pleading for her help.

When a fire claims one of their own, there's plenty of guilt and blame to go around. Lt. Matthew Casey, in charge of the Truck, tries to carry on, but butts heads with the brash Lt. Kelly Severide of the Rescue Squad - and each blames the other for their fallen team member. The firehouse also includes: Battalion Chief Wallace Boden, a fireman's fireman who is confronted by important personal decisions; paramedics Gabriela Dawson and Leslie Shay, who share a close bond and team together to face some of the most harrowing situations imaginable; Peter Mills, an academy graduate who is the latest generation in a family of firefighters; and Christopher Herrmann, a seasoned veteran who loses his home to foreclosure and now must uproot his family to move in with his in-laws.

Severide and Kidd investigate an explosion at a jewelry store. Cruz and Chloe take steps to make Javi a permanent part of their family. Gallo, Ritter and Mouch try to bond with Carver.

After their defibrillator malfunctions on a call, Brett and Violet search for answers. Herrmann tries to find the perfect home for his new recliner. A secret from Gibson's past comes to light.

Violet clashes with her new partner. Severide discovers a hidden stash of money on a call and squares off against the cops working the case. Mouch gets a parking ticket.

After Damon disobeys Kidd's orders on a call, he turns to Severide to protect him. Herrmann searches for the perfect scent to spice things up with Cindy.

Severide gets wrapped up in an Illinois State Police investigation after discovering illegal guns on a call. A bird harasses Mouch on the apparatus floor. Kidd keeps an eye on Carver.

Cruz's past comes back to haunt him. Severide prepares to teach an arson class at the academy. Mouch searches for a victim's next of kin.

Severide investigates an old house fire from 10 years back in which Kidd had responded. Carver and Violet search for a mystery medic who abandoned a victim. Novak looks for a roommate.

A mishap on the aerial ladder in the midst of a fire rescue leaves Mouch shaken and questioning his abilities. Kidd looks for support from Severide while Casey and Brett discuss their future.

Mouch, Gallo, Ritter and Mackey report for training. A nasty blow to the head brings Casey unimaginable pain.

Severide and Kidd work with CPD regarding a suspicious car wreck. Hawkins and Violet's relationship is in jeopardy. Chloe and Cruz adjust to a new family dynamic.

Herrmann is tasked with fulfilling a man's dying wish. Kidd reflects on her Girls on Fire program after one of her students graduates from the Fire Academy. A heckler harasses Firehouse 51.

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.

Boden, Ritter, Herrmann and Kidd work together to take down a local politician responsible for a chemical fire. After his aunt's accident, Gallo worries about their future.

Carver deals with the fallout of his arrest. Brett searches for closure with the baby she rescued. Capp weasels his way into the Firehouse 51 group chat.

Julia spends a couple of days at 51. Boden's stepson returns, desperate for Boden to help his mother. After a little girl starts a fire in her backyard, Kidd and her team decide to dig deeper.

Severide and Van Meter investigate a fire at a family-owned restaurant. Pascal questions Kidd's leadership.

Kidd and Severide investigate a trucking company responsible for a string of accidents. Herrmann recruits Kylie to help get new radios. Firehouse 51 celebrates Violet's birthday. Carver's allegiances are torn.

Pascal and Severide revisit the storage facility fire in hopes of uncovering new evidence. Cruz helps Mouch take his studying to the next level. Novak prepares a proposal for Chief Robinson for a whole blood program.

Herrmann investigates the rise in missing fire hydrants and teams up with Kylie to track them down. Kidd's cousin comes to town, revealing surprising family history. Violet and Novak treat the victim of a birthday cake smash gone awry.