Lt. Severide has his strong ideas on who the serial arsonist is, but first needs to find proof to back up his suspicions. Meanwhile, Lt. Casey adjusts to his new lifestyle in the wake of recent events and Molly's bar is failing, much to the dismay of owners Hermann, Dawson and Otis. Elsewhere, Dawson goes out on a date with Jay Halstead, one of the bar regulars, and Mouch's campaign trail starts to get on track with the aid of Isabella, an old friend of Dawson's.

Boden's future with Firehouse 51 is on the line and McLeod keeps on him about his past wrongdoings, pushing him toward an early retirement. With Boden considering his options, McLeod calls on an unlikely candidate to potentially replace him as Chief. Meanwhile, it becomes clearer who the mole inside the firehouse is and everyone takes measures to make their disdain for him known. Meanwhile, Shay's social life is in full bloom and Arthur continues to take money from the struggling Molly's.