The story of firefighters in Chicago. Following the apartment fire explosion with everyone inside, everyone at Firehouse 51 survives, Mills with a broken leg, but Shay is killed on scene leaving everyone mourning her loss. The episode forwards to six weeks later where we find many in the Firehouse have taken her death hard. Severide, having been on leave after the incident is now AWOL, eventually Casey finds him at his cabin where he admits he;;;s reluctant to return. Also, Casey continues to butt heads with Lieutenant Welch at Truck 66, Boden and his wife double date with Mouch and Trudy.