Dispatch alerts everyone at the FDNY vs. NYPD Hockey Game to a fire in progress and tragedy strikes when a large explosion at the burning building kills Captain Frank Smith. Mac and Flack find infamous arsonist Leonard Brooks at the scene, but he claims that he is being framed. They reluctantly accept Brooks' offer to be the arson investigator on the case. While examining footage of the audience onlookers at the fire, Jo and Adam notice a firefighter with a different precinct number on his hat and discover he is an imposter. After Mac rules him out as a suspect, Brooks becomes the renewed target when they find him at the scene of another fire. Dr. Hawkes lifts prints off of a glove recovered near the ignition point that match Eva Mason, a woman with a history of studying the psychology of pyromaniacs and a criminal record detailing previous arrests for arson. Lindsay uses the logo on a sewing kit she also finds near the ignition point to trace the motel Mason stayed in, and there the team finds her display of Brooks work, the components used to create the two fires, and a camera feed of Brooks' apartment in which they see her holding him at gunpoint. Mason harangues Brooks for helping the police and explains that she set the fires in hopes that he would be proud of her. Understanding that she does not want to be saved from her pyromania, Brooks manages to disarm her and jump out of the window before the ignition point she had rigged in his apartment goes off. Meanwhile, Mac experiences flashbacks of his aphasia diagnosis and expresses his gratitude towards Christine.