For the firefighters, rescue squad and paramedics of Chicago Firehouse 51, no occupation is more stressful or dangerous, yet so rewarding and exhilarating.

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.

When the drunk driver who hits a car and paralyzes a 16-year-old boy turns out to be the son of a dirty cop, Lieutenant Casey must decide whether or not to turn him in. Facing pressure and subsequent threats from the powerful and well-connected Detective Voight, Casey decides to tell the truth, inviting a stand-off. Additionally, Severide, who's fighting off the advances of the Chief’s new assistant, learns he has a fractured vertebra in his neck that may never heal if he doesn't get treated, but ignores the doctor's advice so he can continue working. Meanwhile, Mills is torn between helping his mother at her restaurant and devoting himself full-time to the fire department, like his father did.

Chief Boden is accused of leaving a homeless man to die in a warehouse fire after ordering his men to evacuate the scene, creating negative press and bad feeling within the department. Meanwhile, Lieutenant Severide helps an elderly woman facing some neighborhood problems. Detective Voight ramps up his intimidation tactics aimed at Casey in an attempt to discourage him from testifying against his son. Shay is forced to revisit her heartbreak over her ex-girlfriend Clarice, when she finds herself face-to-face with the ex and her husband during a call. Hermann’s temper flares during a rescue call at a Halloween block party.

Casey confronts Detective Voight 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, an old flame and pharmaceutical rep, hoping she might be able to help alleviate his injury problems.

Facing suspension, Dawson gets a hand from the same girl she saved through the procedures that landed her in front of the disciplinary board. Lieutenant Casey finds his fuse shortening as Detective Voight stops at nothing to get him to retract his statement. However, when Casey lays his life on the line during an apartment fire, he may have unknowingly caught the break he was needing.