A series of mysterious gas leaks has members of Firehouse 51 puzzled and spread thin. Brett’s conflicted when her birth mother gets serious about finding her. Severide misunderstands his role as Cruz’s best man. Mouch bites off more than he can chew.
The surprising arrival of a new fire truck brings both joy and chaos to members of Firehouse 51. Boden and Severide are asked to make peace with an old foe for the greater good. Brett receives family news. Foster plans a party with friends.
A series of false alarms at a private school hinders 51’s ability to respond to legitimate emergencies. Kidd asks for ideas to surprise Severide on his birthday. Cruz and Brett rent out their extra room but get more than they bargained for.
A pest control problem forces the 51 team to temporarily bunk with Firehouse 20. Casey clashes with Delaney. Foster, Kidd and Brett fear Leone has it out for them. Boden mulls a procedural overhaul.
Members of Firehouse 51 are dismayed to learn their boundaries have been redrawn to overlap with an adjacent station, and problems quickly arise. Casey and Gallo hunt a missing piece of equipment. Brett and Foster find themselves at odds.
An unexpected visit throws Casey for a loop. Severide sets out to exonerate a wrongly convicted arsonist. Kidd pays the price for burning the candle at both ends. Cruz goes on a mission to fix one of Otis’s old toys.
Severide starts off on the wrong foot at his Office of Fire Investigation assignment when, despite orders, he reopens an old case. Herrmann is on a mission to discover what caused an apartment fire. Kidd finds herself burning the candle at both ends.
Severide must make a tough decision about the future of his career at Firehouse 51. Herrmann deals with the consequences of his temper. Cruz is excited to demonstrate the Slamigan at the Firefighting Expo. Commissioner Grissom returns.
Cruz and Severide suspect foul play when a fire started by an elderly woman turns deadly. Kidd, Foster and Brett create a women’s-only lounge. Firehouse 51 celebrates some good news.
Kidd must prove herself at the National Firefighter Leadership Conference while the rest of Firehouse 51 is called to two eerily similar car wrecks. Mouch tries to keep everyone in the firehouse informed by starting a newsletter, but things quickly get out of hand. Cruz deals with a heartbreak.
A rare but deadly bacteria takes its toll on numerous victims around the city, leaving Chicago’s finest first responders to work together alongside the CDC to resolve the dangerous situation. Following a fire at a local university that ties into the outbreak, Severide has suspicions that something bigger is happening.
Brett and Foster question the suspicious circumstances surrounding an attack at a juvenile detention center. A convoluted new technology at Firehouse 51 tests everybody's patience. Kidd is chosen to represent the district at a leadership conference.
Lt. Casey struggles to get Chief Boden to sign off on an energetic new recruit. Against her better judgment, Foster extends an olive branch to her irritating new medic. Otis inspires Herrmann to seek new partners at Molly’s. Brett realizes life in Fowlerton will take some getting used to.
The mattress factory fire spirals out of control. Truck and squad lay it on the line in hopes of getting the trapped victims out alive.