After a harrowing game of cat and mouse that led to the capture of serial killer and cult leader Joe Carroll (James Purefoy) in Series Two, Ryan Hardy (Kevin Bacon) has finally moved on. He's returned to the FBI to work with his niece, Max Hardy (Jessica Stroup), and partner, Mike Weston (Shawn Ashmore), and he's found new love with Dr. Gwen Carter (Zuleikha Robinson). But Ryan's happiness is quickly shattered when another threat arises to tear open old wounds and expose the sins of the past. With Joe awaiting execution, the team must unravel a twisted matrix of murder before it destroys them all. Behind it lies a horrifying possibility: Can someone even more dangerous than Joe Carroll be at large?