Sean O'Neal surprises Det. Upton with a call from prison, revealing sensitive information. While Upton grapples with how to keep O'Neal at a distance, the team quickly mobilizes to stop a crime in progress before it's too late.

After a brutal shooting, Burgess and Ruzek find themselves trapped aboard the busy "L" subway train. As they piece together scant evidence, the team is drawn into a dark family drama. Burgess' proximity to the shooting triggers harsh memories.