A new recruit with ties to the CFD tests Severide's patience; Violet receives a mysterious note that sends her and Brett on a hunt for the person who wrote it.
A fire breaks out at a pet food factory, and Casey and Severide help the owner, Pete, get to the bottom of it; the annual garage sale takes place at 51 and everyone is on edge.
Members of the firehouse are frustrated with their inability to help Chief Boden, whose job is on the line pending an internal investigation in the aftermath of a complicated call to a fire; Lt. Severide struggles to accept his smaller role and adjusts to the presence of Capt. Patterson, his new commanding officer; Dawson shakes things up on the work front and Casey attempts to find a crucial piece of evidence in his ongoing investigation against Nesbitt.