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.
Vasquez fights to prove himself at 51; Violet and Novak pursue a troubling mystery; Herrmann is on a quest to keep Molly's profitable.
When city budget cuts stretch crews thin, Pascal takes matters into his own hands; Vasquez looks to an old friend for help; an incident in the field hits close to home for Violet.
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.
Cruz hunts for the identity of an unknown ally; Mouch takes steps to help a friend; Vasquez must make a difficult choice.
A traffic jam forces Violet and Novak to take drastic measures to save a patient; Severide shadows Pascal for a day; Kidd goes the extra mile for Isaiah.
Severide investigates a suspicious high school fire; Novak gets an unexpected call; Violet brings a 51 firefighter onboard the ambulance for a shift.
When an act of arson harms someone close to the Firehouse 51 family, Severide must track down the perpetrator; impending budget cuts push Mouch and Pascal to get creative.
A member of the Firehouse 51 family remains in peril; Cruz lends a hand to Severide in the ongoing investigation.
Herrmann grows uneasy when a local accident attorney inserts himself into a routine call; Firehouse 51 gets a visitor.
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.
Javi spends a couple of shifts at Firehouse 51; Kidd and Carver work together to help Carver's former boss; as Hawkins and Violet's relationship blossoms, Gallo turns his attention elsewhere.
Kidd recruits Carver, Capp and Tony to help prepare her new lieutenant's quarters; Severide and Detective Pryma reluctantly pair up to work a police investigation; Firehouse 51 comes together to fight a movie theater fire.
Kidd gets a glimpse into Carver's chaotic personal life; Mouch and Herrmann receive an unexpected gift.
Firehouse 51 hosts a Halloween open house; Kidd and Severide help a young girl after she gets kicked out of her home.
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.
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.
A video of Casey from the roof rescue goes viral; Mouch sets up a Little Free Library at Firehouse 51; Herrmann breaks protocol.
Griffin learns the truth about his father's death and reveals why he really came to visit Casey; Gallo, Ritter and Violet take steps to expand their microbrewery business.
Kidd spreads her wings as a lieutenant; Chief Hawkins rides with Ambulance 61 to learn more about Brett; Casey takes a trip out of town; a Ritter date night turns into an emergency situation.
Casey makes a life-altering decision; Gallo, Ritter and Violet agree to an interview and photo shoot; Brett and Mouch launch the paramedicine program; Cruz comes closer to fatherhood.
A major security breach in the city's computer networks forces Firehouse 51's senior leaders to take matters into their own hands; Severide gears up for an arson investigation.
Gallo clashes with the new lieutenant temporarily filling in for Casey; Severide closes in on a dangerous and deadly arsonist.
Gallo, Violet and Ritter debut their microbrewery business at Winterfest; Brett prepares to present her paramedicine program to an oversight panel; Firehouse 51 gets in the holiday spirit.
Stella Kidd returns to Firehouse 51; the team must work together to put out a potassium fire in a tunnel; after that incident, Ritter begins to worry about a young cop who witnessed the fiery death of a truck driver.
On a call with Station 37, a firefighter is struck by a power line and decides to lash out after her injury; Brett is visited by Scott and Amelia; Violet gets a surprise envelope; the rest of 51 enters a contest.
Chief Hawkins goes above and beyond to help Brett and Violet with a problem; Kidd pursues an open lieutenant position; a blast from the past asks Mouch and Herrmann for a favor.
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 open spot on Truck 81; a possible new recruit to 51 gets tested at a call.
Cruz forms a bond with a young immigrant boy he meets while fighting an apartment fire; Squad makes plans to prank the newest member of their team; Hawkins and Violet struggle to keep their relationship a secret.
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.
Firehouse 51 must band together when one of its own is taken hostage.
Firehouse 51 tackles a fire caused by a dropped jet engine, and one of their own is accused of a theft related to the incident; Kidd and Boden disapprove of Kylie's potential new love interest.
A family friend asks Herrmann for some advice on opening a bar; tensions run high between Emma and Violet; Kidd struggles to keep her team together.
Mouch and Ritter work together to solve a murder mystery; Severide and Cruz tackle a food truck fire; Gallo goes to see Hawkins about Violet.
The big wedding day arrives and Firehouse 51 welcomes Casey back to celebrate the joyous occasion; Emma's plans to replace Violet come to a shocking end.