After putting out a kitchen fire in an upscale townhouse, Casey, Herrmann, Mouch, Cruz, Otis and Mills find themselves accused of stealing a $50,000 diamond necklace from the home, touching off an internal investigation. Cruz’s brother Leon is caught in the middle of an escalating gang war, leaving Cruz to make a desperate choice to save him. Meanwhile, Dawson invites Casey to her cousin’s fancy Christmas party, and a frustrated Shay has reached her limit with Severide.

Lieutenant Severide is anxious to implicate the serial arsonist, while Dawson and Shay get a shock on a routine call. Meanwhile, suspicions continue to point to Clarke as the mole inside the firehouse and Molly's falls deeper into the red. Elsewhere, Mouch campaigns for union president, with the aid of Isabella, and Boden butts heads with Gail McLeod.

While out on a jog, Severide comes across a secluded and empty construction site and encounters a young boy who has been trapped in a backhoe loader and is in dire need of assistance. Boden and McLeod continue to butt heads about the future of the firehouse and Boden breaks news about his future to Casey. Meanwhile, it's election day for the union presidency and Mouch and Greg Sullivan have a debate on Otis' podcast. With rival bar Game Day's future in peril, the finger is being pointed at Molly's.

Two firehouse members are abducted, triggering a desperate search by the Chicago P.D. Elsewhere, Casey and Dawson struggle to balance their personal and professional lives, and Chief Boden deals with news that his newborn has potential complications.