An investigation into a string of murders possibly related to a Colombian drug gang.
Thanksgiving at the firehouse includes a 10-car pileup, a gang shooting, and a meth lab.
Lt. Kelly Severide tries to keep his shoulder injury a secret as he helps a construction worker from a collapsed building. Meanwhile two teenagers are stuck in a vehicle.
The members of Firehouse 51 struggle to cope when one of their own dies in a fire. Lt. Matthew Casey and
Lt. Kelly Severide blame each other for their friend's death. Meanwhile Casey goes through a separation with Hallie and
Battalion Chief Wallace Boden has to make a crucial decision.