Tragedy strikes when a rescue attempt at a tenement building proves unsuccessful, leaving the men and women of firehouse 51 affected by the loss of the victim. Severide's decision to put Mills on the fast track to move from Truck to Squad doesn't sit well with some of the others and tension mounts between Severide and Casey over Heather Darden. Shay and Dawson are forced to deal with a junkie's crazy behavior while on a call and Shay considers a different way to have a family. Meanwhile, the team draws the ire of local drug dealers who threaten the peace and safety of the neighborhood and firehouse.

Mills finds himself the target of resentment from some colleagues when Severide supports his desire to join Squad. Tara, a paramedic candidate, joins Dawson and Shay on the job for a few shifts. Meanwhile, Shay comes to the aid of Cindy Herrmann, who suffers from pregnancy complications while her husband Christopher is out of town. Elsewhere, Dawson and Casey draw closer as the grand opening of Molly’s draws near, and Casey receives a surprise visit.

Accused of sexual misconduct by a former paramedic candidate, Severide faces potentially dire consequences and fights for his survival both within the Chicago Fire Department and the legal system. Detective Voight returns, looking to collect on the favor that Dawson owes him for helping her brother, Antonio. Casey falls back into old patterns in his personal life, while Dawson, Herrmann and Otis become the proud owners of a real neighborhood bar as Molly's prepares for its grand opening.

A frustrated Severide, turns to an unlikely ally to resolve his current dilemma. Casey begins to find satisfaction in his personal life, while Mills and Dawson face personal challenges. Meanwhile, the squad is called to the scene of a harrowing apartment building collapse.