As the 15th Division attempts to recover from an explosive event involving one of their own, a series of arsons culminates in the torching of a laundromat. The list of suspects grows, as Chris and Gail take to the streets and encounter a man from Chris's past, while Traci interrogates a young firebug found at the arson scene. Meanwhile, Andy's effort to stop the grieving widow from entering the burnt-out laundromat resultS in the two women being trapped in the unstable building, and what seems like a straightforward case of arson ends up being something much bigger.

When a police informant's murder points to the involvement of the notoriously brutal East Jameson gang, the division realizes that cracking this case will not be easy. And when Gail's intimidating mother, Superintendent Elaine Peck, arrives on the scene, there is even more pressure to solve the case. Meanwhile, Andy finds herself paired with Detective Rosati, whose unintentional disclosure of a secret puts Andy's relationship with Luke in jeopardy. And Gail, stressed out by her mother's presence in the station, is assigned to protect the only known witness to the crime -- a seemingly homeless eight-year-old boy with a shocking secret of his own.