Firehouse 51 is forced to share space with Firehouse 17. Kidd and Herrmann fight over Ritter; an arson case tests Kidd and Severide's relationship. Firehouse 51 says goodbye to one of its own.

Mouch sets out to change his legacy and nickname. Ritter pushes Herrmann to see a doctor. Brett searches for the perfect wedding venue.

Brett and Violet decide to take the investigation into their own hands, after witnessing a domestic dispute. Mouch vets Truck 81's new firefighter. Herrmann relies on something new to aid him on the job.

Julia spends a couple days at 51. Boden's stepson, James, returns desperate for Boden to help his mother.

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.

Firehouse 51 welcomes back some familiar faces and says goodbye to Brett. Violet scrambles to decorate Brett's wedding venue. A call at the expo center takes a shocking turn.

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

A hazmat call at a dialysis center leads to a shocking discovery; Boden clashes with Paramedic Chief Robinson; Carver notices a concerning change in Gibson's behavior.

Severide, Kidd and Van Meter investigate a fire at a recording studio. Kylie helps James keep a secret from Boden. Mouch struggles to maintain boundaries with a paramedicine client.

Severide is in charge in Boden's absence. A possible wrench is thrown into Cruz' adoption of Javi. Violet asks a floater to become permanent at 51. Christopher goes too far with safety of his kids. Funding for Girls on Fire is withdrawn.

Severide goes for an unexpected ride on Truck 81; Ritter's worlds collide when his secret cop boyfriend helps 51 track down Severide and the missing rig.

Severide and Violet risk clashing with Chief Robinson after Lennox makes a dangerous decision on a call. Cruz and Chloe's marriage problems come to a head.

Boden makes a decision that impacts the race for deputy commissioner; a tense call brings up painful memories for Carver and Damon; Mouch struggles to adjust to the new truck.