Evidence recovered at a series of fires indicates that Lt. Severide (Taylor Kinney) is being targeted by an arsonist. Meanwhile, Battalion Chief Boden (Eamonn Walker) clashes with Gail McLeod (guest star Michelle Forbes), a high ranking consultant with the State Marshal’s office who keeps a sharp eye on budgets and performance at the city’s firehouses -- and has 51 under her microscope as one that could face the prospect of being closed. Elsewhere, Lt. Casey (Jesse Spencer) reflects on the year anniversary of Andy’s death, Shay (Lauren German) has suspicions about Severide’s paternity and Mouch (Christian Stolte) enjoys a visit from Mari (guest star Cindy Chang), his Japanese girlfriend.
In the wake of Heather’s (guest star Chaon Cross) incident, Lt. Casey (Jesse Spencer) is having a hard time handling his newfound responsibilities. Lt. Severide (Taylor Kinney) is on edge dreading the next attack from the firehouse’s arsonist. Meanwhile, with Renee (guest star Sarah Shahi) back from her mother’s, Severide knows he has to confront her about his paternity suspicions. Elsewhere, Mouch (Christian Stolte) begins his campaign for union president and Shay (Lauren German) and Dawson (Monica Raymund) feel that they need to get out more.