While responding to a potential carbon monoxide leak inside a home, Lt. Severide and Cruz uncover the remains of a child inside the chimney. Subsequent information leads Severide to believe that the discovery may be linked to a case he had worked on years ago. Meanwhile, with election day nearing, Casey braces for the worst in his run for Alderman, prompting Dawson to enlist the firehouse team to lend a hand to the cause. Complicating his chances, Alderman Becks continues to bad mouth Casey to the press, but an incident in the field might prove beneficial