Severide finds that he shares a familiar past with Eric Whaley, the Lieutenant who was brought into the firehouse to help out. Dawson lets Shay in on her secret, while Casey deals with family issues. Meanwhile, a bad batch of heroin on the streets has Boden and the team scrambling, while Clarice 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.