L.A. Detective Sam Dietz (Leo Rossi), struggling to emotionally survive his previous big case (from in the first ''Relentless'' film) is unwillingly paired with a shady FBI agent Kyle Valsone (Ray Sharkey), during a case tracking another serial killer (Miles O'Keefe), who kills seemingly at random. But every time Dietz gets a lead, Valsone gets in the way and somewhat throws off the investigation. Suspecting more than meets the eye, Dietz goes around the law to learn the identity of the killer and find out what Valsone is hiding and his connection to the killer. Meanwhile, Dietz's wife Carol (Meg Foster) now estranged from him due to his long hours, tries to deal with her current situation and their uncertain future.