The story of firefighters in Chicago.
Cast: Jesse Spencer, Taylor Kinney, Monica Raymund, Lauren German, Charlie Barnett, Yuri Sardarov, Christian Stolte, Eamonn Walker, Anne Lockhart, David Eigenberg, Joe Minoso, Randy Flagler, Don Kress, William Smillie, Steve Piper, Teri Reeves, Mo Gallini, Nicole Forester, Kathleen Quinlan, Anita Nicole Brown
Casey puts his life on the line and digs deeper into the shady dealings of Jack Nesbitt. With members of truck and squad at odds over Rice actions in the field, Chief Boden is left to figure out how to create unity in a divided house, while Severide comes to question his own judgment.
At Sgt. Voight's urging, a determined Lt. Casey agrees to go undercover in an effort to provide proof of Jack Nesbitt's shady dealings. Meanwhile, Otis and Severide continue to disagree about the integrity of Scott Rice, causing tensions to flare between members of truck and squad. Meanwhile, Herrmann helps out a fellow member of the firehouse.
An apartment fire connected to a case of rape and attempted murder resembles an unsolved case in New York, so Sgt. Benson of Special Victims Unit comes to Chicago to help Intelligence with the investigation.
Mills tries to save a driver who's been seriously injured in a car accident. Meanwhile, Casey has doubts about the owner of a remodeled strip club and Hermann, Otis and Cruz prepare for the peewee hockey championship.
It's all hands on deck when Firehouse 51 races to the scene of a deadly chemical leak inside an industrial building. With squad and truck tested like never before, scores of workers are rescued but many are experiencing respiratory distress. This prompts truck 81, squad 3 and ambulance 61 to spring into action to transport the victims to nearby Chicago Med. The situation takes a turn from bad to worse in the midst of the chaos when a "patient" planted inside the hospital goes on a suicide mission armed with a grenade and claiming to be the carrier of a deadly airborne disease. Trying to stop the madman from engaging the explosive device, a member of the firehouse team is severely wounded in the blast and left to face life-threatening injuries. With no other choice, Chicago Med is forced into lockdown until doctors and the Hazmat team can determine the severity of the airborne virus.
During a harrowing call to a structure fire, Herrmann rescues a trapped toddler, but the questionable circumstances surrounding the event sends him on a personal mission to locate the father and get to the bottom of the situation. Severide makes up for lost time by retracing key friendships from his adolescence, while Mills discovers some surprising news. Elsewhere, Cruz and Brett's relationship comes to a crucial juncture, while Otis develops some unexpected feelings.
Lt. Severide lobbies Chief Boden for a favor for Scott Rice, an old friend needing a second chance with the CFD, but Casey and Otis have their doubts. Elsewhere, Mills works to regain his active squad status while Brett and Dawson decide they need a big night out.
The interim chief makes a tactical error during an apartment fire, stirring up tensions and putting careers in jeopardy.
Interim Chief Pat Pidgen is brought over to temporarily fill in for Boden, who is left to tend to his personal affairs. When tension is sparked as the result of his derisive leadership, the absence of Chief Boden becomes all too apparent. Meanwhile, Lieutenant Severide must deal with a most unwelcome addition to his squad, Brett gets closer to a girl she previously rescued and Casey starts seeing a new woman, Beth, but interesting complications quickly unfold.
Mills and Brett race to recover a missing teenager and are left stranded in the unforgiving elements, while the rest of Firehouse 51 babysits an abandoned newborn. Meanwhile, Lt. Severide receives an interesting job proposal and Chief Boden finds himself at odds with his father over his treatment and the planning of a big party in his honor.
More clues emerge about the fire that killed Shay, leading Severide to a former nemesis; Shay's sister visits; Cruz is faced with a surprise; Boden tries to help his father.
Severide and Dawson discover startling evidence found at a storage unit fire that appears connected to the fire that took Shay's life. Meanwhile, the firehouse bands together when Chaplain Orlovsky is the victim of a bad car accident.
The firehouse receives unsettling news when two of their own come up missing following a routine call, prompting members of Chicago P.D. to lead the search. Meanwhile, Casey and Dawson have a hard time figuring how to juggle their personal and professional lives. Elsewhere, Chief Boden and Donna struggle with news that their newborn has potential complications and they receive a surprise out-of-town visitor.
A house fire sees the team attempting to save the lives of a couple trapped inside. Chief Boden prepares to start his new family. The combination of life at work and home sees Casey and Dawson drifting apart.
Dawson and Casey's relationship is tested as the team responds to a truck leaking hydrochloric acid in a busy intersection. Severide learns about Brittany's past. Mouch has dating troubles.
The members of the firehouse spring into action when a helicopter explodes over a populated area.
During a house fire, Firehouse 51 rescues the owner from the cellar clutching a suspicious box, leading Lt. Severide to bring in Sergeant Voight and Detective Lindsey for further investigation.
Casey faces his corrupt brother-in-law and Brett goes above and beyond to help a mother in need. Meanwhile, Mills get an education on unlicensed private investigation and Dawson begins training with Herrmann.
Lieutenant Casey deals with the fallout of his sister Christie’s impending divorce. Meanwhile, Dawson and Mills settle into their new roles at Station 51. Elsewhere, Brett can’t decide if she wants to leave Chicago and the Molly’s crew still can’t figure out how to get the food truck started.
Dawson starts her first day as a candidate and looks to find a balance with Lieutenant Casey inside the firehouse. Mills must come to terms with a future that doesn’t include the squad. Meanwhile, Severide confronts his demons in an unexpected way and the Molly’s crew has a date with the city inspector to make sure their food truck is up to code.
Fingers get pointed and tempers flare between members of Firehouse 51 and the Austin firehouse when fire trucks collide en route to a perilous call. Meanwhile, Boden has a plan to get Dawson her badge, but it comes at a cost. Elsewhere, Mills confronts his past and his future on the same day and the Molly’s crew hits some hurdles starting up their new food truck.
Lieutenant Severide returns to Firehouse 51, but he is clearly not his usual self and Dawson counts down the weeks until she gets started as a candidate at the Austin Firehouse. Meanwhile, Mills learns more about his father’s family and Herrmann asks the rest of the Molly investors to come up with some new ideas to turn the business around.
Boden forces members of Firehouse 51 to pull themselves back together in the aftermath of a harrowing fire explosion. While Severide goes missing for one week too many, Casey works to track down his whereabouts. Meanwhile, Newhouse brings some unexpected news regarding one of Mills’ relatives while Herrmann and Otis make some new goals regarding Molly’s.