Firehouse 51 is forced to share its 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.

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

Julia spends a couple of days at 51. Boden's stepson, James, 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.

After their defibrillator malfunctions on a call, Brett and Violet search for answers.

Firehouse 51 welcomes back some familiar faces and says goodbye to Brett. Violet scrambles to decorate Brett's wedding venue.

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.

A hazmat call at a dialysis center leads to a shocking discovery.

Severide, Kidd and Van Meter investigate a fire at a recording studio.

Severide steps in as ranking officer at 51. Kidd fights to save her Girls on Fire program.

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 Paramedic Chief Robinson after Lennox makes a dangerous decision on a call.

Boden makes a decision that impacts the race for Deputy Commissioner.