The show explores the lives, both professional and personal, of the firefighters and paramedics of the Chicago Fire Department at the quarters of Engine Co. 51, Truck Co. 81, Rescue Squad Co. 3, and Ambulance 61. Following the death of Firefighter Andrew Darden, the loyalties fracture and divide as the Lieutenant, or officer-in-charge of Truck Co. 81, Matthew Casey and the officer-in-charge of Squad Co. 3, Lieutenant Kelly Severide both blame one another for Darden's death. Kelly Severide is consumed with more guilt when he learns Darden's wife also blames him for the tragedy. Despite their differences, the firehouse comes together after the near death of Truck Co. 81 Firefighter Christopher Herrmann.