Severide (Taylor Kinney) finds that he shares a familiar past with Eric Whaley (guest star Shane McRae), the Lieutenant who was brought into the firehouse to help out. Dawson (Monica Raymund) lets Shay (Lauren German) in on her secret, while Casey (Jesse Spencer) deals with family issues. Meanwhile, a bad batch of heroin on the streets has Boden (Eamonn Walker) and the team scrambling, while Clarice (guest star Shiri Appleby) and Shay find they have a new problem to overcome. Charlie Barnett and David Eigenberg also star. Kathleen Quinlan and Jon Seda also guest star.