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.
Novak explores a new romantic connection; Vasquez deals with the aftermath of his father's recent release.
Pascal finds himself under intense scrutiny when a member of the firehouse is injured on a call; Herrmann grapples with family issues.
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.
Detective Pryma asks for Severide's help on a case involving explosives; Gallo and Carver clash.
Severide struggles with the cost of helping Det. Pryma with the Martucci case; Gallo campaigns for Herrmann to represent 51 at the National Firefighter's Association's Winter Conference; a familiar face makes a shocking return.
Detective Pryma's case comes to an explosive end with Kidd and Carver's lives in danger; Brett installs an infant safe surrender box at 51; Violet is determined to take Emma down.
Firehouse 51 prepares for their semi-annual firehouse inspection; Brett fights to save her paramedicine program; Commander Martin Pearce asks Severide for a favor.
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.
Firehouse 51 helps Herrmann put on a school fundraiser; Carver's troubled brother comes to town; a grateful citizen is determined to thank Brett and Severide for saving his life.
An annoying floater takes a romantic interest in Violet; Ritter catches a local politician in a compromising position; Mouch and Severide help Trudy with an arson investigation.
Kidd, Seager and Carver investigate a fire at the city stables; Kylie clashes with some of the firefighters over changes due to budget cuts; Herrmann struggles to keep it together as Cindy's condition worsens.
Cruz feels the burden of his increased responsibilities; Kidd, Gallo and Carver get caught in the middle of a gang war on a call; Herrmann wrangles Trudy for help lifting Cindy's mood.
Mouch builds a classic firetruck model for the Deputy District Chief but needs 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.
A familiar face returns to Firehouse 51 to serve with Kidd on a special task force; with Tony close to breaking the CFD's perfect attendance record, Mouch and Capp work to keep him safe; old grudges resurface when Gallo reunites with a family member.
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; Brett steps in to perform Dylan's magic show when he's out of town.
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.
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 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.
Severide and Herrmann clash over office space; Boden looks at Pelham's past as he considers making him permanent; Gallo's resentment of Pelham comes to a head; Brett and Ritter force Violet to confront her true feelings for Gallo.
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.