The pressure to perform on such a high level has a way of taking a personal toll, sometimes putting team memebers from the Truck and the specially trained Rescue Squad at odds with each other. Despite any differences, this is an extended family, and when it's go time, everyone inside Firehouse 51 knows no other way than to lay it all on the line for each other. When tragedy claims one of their own, there's plenty of guilt and blame to go around. Lt. Matthew Casey, in charge of the Truck, tries to carry on, but butts heads with the brash Lt. Kelly Severide of the Rescue Squad - and each blames the other for their fallen team member. Adding to the turmoil, Casey, unbeknownst to his colleagues, is in the midst of a separation from Hallie.