At the site of a train accident, Peter Mills becomes deeply upset when he observes the dead body of a young victim. Unable to shake his emotional distress about the event, he questions his future as a firefighter. Dawson and Shay save a 6-year-old girl whose mother is abusing her – but their confrontation leads the woman to resort to dire actions. Meanwhile, Severide aggravates his injury while rescuing a heart attack victim and Shay sends Clarice, her married, pregnant ex-girlfriend, back home to her husband.

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.

Eaten up by his guilt over Flaco’s death in the fire, Cruz goes to Casey to confess. While Shay recovers from a head injury sustained in the ambulance crash, Severide asks Dawson for her help in dealing with his own injury. Casey is caught in the middle of a family conflict between his mother and sister. Elsewhere, Herrmann finds a business deal hard to stomach.

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, the troubled teenage firebug he’s been trying to help, and his Uncle Ray. Meanwhile, Severide decides on his future and reaches out to his father. 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.

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.

Casey deals with the aftereffects of his sister's divorce announcement. Dawson and Mills get used to their new roles at Station 51. Brett ponders whether to leave Chicago. The Molly's crew works to get the food truck started.

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.

Mouch, Gallo, Ritter and Mackey report for training. A nasty blow to the head brings Casey unimaginable pain.