When a fire claims one of their own, there's plenty of guilt and blame to go around. Lt. Matthew Casey, in charge of the Truck, tries to carry on, but butts heads with the brash Lt. Kelly Severide of the Rescue Squad - and each blames the other for their fallen team member. The firehouse also includes: Battalion Chief Wallace Boden, a fireman's fireman who is confronted by important personal decisions; paramedics Gabriela Dawson and Leslie Shay, who share a close bond and team together to face some of the most harrowing situations imaginable; Peter Mills, an academy graduate who is the latest generation in a family of firefighters; and Christopher Herrmann, a seasoned veteran who loses his home to foreclosure and now must uproot his family to move in with his in-laws.

Severide is hiding a serious shoulder injury sustained in the fire that killed Andy Darden, and grapples with his guilt as he fights to rescue a construction worker trapped in a building collapse. Adding to the burden, Darden's wife Heather turns on Severide at the annual firefighters' barbecue, blaming him for her husband's death. A call is made to an accident site at Hancock Tower, where two teenagers are pinned in a vehicle trapped beneath the falling debris of a broken window washer's cart. Meanwhile, Casey and Hallie work to figure out their future together.

Casey faces pressure to cover for a cop's son, who was responsible for a drunken-driving accident that left a teenager paralyzed. Meanwhile, Severide ignores his doctor's warnings that his neck injury may never heal if he doesn't seek treatment; and Mills must choose between working at the fire department full-time or helping his mom with her restaurant.

Chief Boden is plagued by bad press and low morale in the department after being accused of leaving a homeless man to die in a warehouse blaze. Meanwhile, Severide helps an elderly woman; Det. Voight continues to intimidate Casey; Shay runs into her ex-girlfriend during a call; and Hermann gets angry during a Halloween rescue.

Casey confronts Detective Voight (Jason Beghe) about his harassing tactics, vowing never to back down, and ends up paying the price for his decision. Dawson faces disciplinary action for her on-the-job conduct. Meanwhile, Severide finds his arm failing him during a rescue at a construction accident, and reaches out to Anna (Mouzam Makkar), an old flame and pharmaceutical rep, hoping she might be able to help alleviate his injury problems.

Casey risks his life during an apartment-fire rescue, potentially earning a much-needed break from Det. Voight's ongoing pressure to retract his statement. Meanwhile, Dawson gets help from a girl she saved.

Everyone in the firehouse is ordered to take a drug test after a call to a daycare center exposes them to a makeshift meth lab, and Severide stalls, not wanting his injury, or the painkillers he takes, to be discovered. Meanwhile, Truck and Squad find themselves pinned down by gunfire while trying to help the victim of a gang shooting, and a deep-fried turkey fire grows from small to explosive when a garage catches fire. Elsewhere, Dawson saves a bleeding man and Casey delivers a baby on the scene of a massive car pileup on the freeway.

Peter is deeply upset when a young victim is discovered at the site of a train accident; an abusive mother takes dire actions; Severide's injury is aggravated.

Jose Vargas is forced to go on disability after sustaining an injury in a fire; Severide receives a tempting invitation from a woman he saved from a car crash; Cruz tries to end his brother's involvement with a gang.

After putting out a kitchen fire in an upscale townhouse, Casey, Herrmann, Mouch, Cruz, Otis and Mills find themselves accused of stealing a $50,000 diamond necklace from the home, touching off an internal investigation. Cruz’s brother Leon is caught in the middle of an escalating gang war, leaving Cruz to make a desperate choice to save him. Meanwhile, Dawson invites Casey to her cousin’s fancy Christmas party, and a frustrated Shay has reached her limit with Severide.

Severide finally addresses Chief Boden about his injury and makes some important personal decisions about his future. Meanwhile, Casey struggles with family matters and Dawson takes matters into her own hands when she discovers a young girl who is the sole survivor at the scene of a rescue call.

A troubled Chief Boden goes to the police when a man dies in a hardware store fire set by Ernie (Cody Sullivan), the troubled teenage firebug he’s been trying to help, and his Uncle Ray (Darrell W. Cox). Meanwhile, Severide decides on his future and reaches out to his father (Treat Williams). Elsewhere, Otis finds camaraderie when he fills in for a few shifts at the slowest firehouse in the city, and makes a decision of his own, while Dawson and Shay find themselves in a bad predicament during a call to a tenement

Severide finds that he shares a familiar past with Eric Whaley, the Lieutenant who was brought into the firehouse to help out. Dawson lets Shay in on her secret, while Casey deals with family issues. Meanwhile, a bad batch of heroin on the streets has Boden and the team scrambling, while Clarice and Shay find they have a new problem to overcome.

Dawson attempts to help her brother Antonio unravel the details of his drugs-and-gang investigation, and goes behind his back in turning to an unlikely source for assistance. Casey and his mother, Nancy struggle with their new relationship. Meanwhile, as a favor to Lieutenant Whaley, Severide visits someone important from his past, while Herrmann and Otis learn some hard truths about their "silent partner" in the bar.

The anguish that haunts Cruz over his previous actions boils over, as he puts himself and his fellow firefighters in jeopardy. Casey and his sister Christie try to solve their issues with their mother and each other. Meanwhile, Severide reaches out again to an important person from his past as a favor to Lieutenant Whaley and the squad gains new perspective after assisting the bomb squad on an extremely dangerous call.

Mills presses Bennie Severide for information about his father's death. Meanwhile, two mysterious diner fires are investigated; and Shay's baby plans take on a new direction.

A rescue attempt at a tenement building ends in tragedy. Elsewhere, tensions run high when Severide decides to prepare Mills for a move from Truck to Squad; Shay and Dawson deal with a junkie's erratic behavior; and the team members have a run-in with local drug dealers.

Despite Severide's support, Mills faces resentment from his colleagues about his desire to join Squad. Meanwhile, a paramedic candidate works a few shifts with Dawson and Shay; Shay helps a pregnant woman who is suffering from complications while her husband is out of town; Dawson and Casey become closer; and Casey gets a surprise visit.

A rescue attempt at a tenement building ends in tragedy. Elsewhere, tensions run high when Severide decides to prepare Mills for a move from Truck to Squad; Shay and Dawson deal with a junkie's erratic behavior; and the team members have a run-in with local drug dealers.

Despite Severide's support, Mills faces resentment from his colleagues about his desire to join Squad. Meanwhile, a paramedic candidate works a few shifts with Dawson and Shay; Shay helps a pregnant woman who is suffering from complications while her husband is out of town; Dawson and Casey become closer; and Casey gets a surprise visit.

A former paramedic candidate accuses Severide of sexual misconduct. Elsewhere, Det. Voight returns to collect on a favor that Dawson owes him; Casey falls back into bad habits; and Dawson, Herrmann and Otis prepare for Molly’s grand opening.

Severide pushes back against the allegations leveled against him, antagonizing Chief Boden and gaining an unlikely ally in the process. Meanwhile, Casey finds personal happiness; Mills and Dawson face relationship challenges; and the squad responds to an apartment-building collapse.

Events force Lieutenant Casey to team up with the Intelligence Unit, now run by Voight, who doesn’t appear to have changed his crooked ways after his stint in prison. Shay's excitement at the prospect of becoming a parent grows, while Mills and Dawson face some personal challenges. Meanwhile, the house comes together to support the opening of Molly's.

When a call comes in from the Cook County jail, the squad steps into a volatile predicament and are tasked with trying to defuse an escalating situation. Shay remains hopeful about her baby dreams and Hermann's wife Cindy goes into labor with their fifth child. Meanwhile, Mills and Dawson face key decisions in their personal lives.