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.