S4, E17: While responding to a potential carbon monoxide leak inside a home, Lt. Severide (Taylor Kinney) and Cruz (Joe Minoso) 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 (Jesse Spencer) braces for the worst in his run for Alderman, prompting Dawson (Monica Raymund) to enlist the firehouse team to lend a hand to the cause. Complicating his chances, Alderman Becks (guest star Armand Schultz) continues to bad mouth Casey to the press, but an incident in the field might prove beneficial.