Nicholas Cage is Tom Welles, a surveillance specialist with a modest, home-based business. Respected but still waiting for the big break that will improve his professional status, Welles spends most of his time on routine cases. Nothing too dangerous, nor too threatening - until a case involving a small, innocuous-looking plastic reel of film turns Welles' life upside down, sending him down a sordid and terrifying path into society's deepest corners.

Drifting away from his family life, Welles is aided by streetwise Max California (Joaquin Phoenix) as he pursues a bizarre trail of graphic and disturbing evidence to determine the fate of a complete stranger. As his obsession with the case grows, Welles enters the seedy world of pornography and sees things beyond his worst nightmares - coming to realise how far-reaching and deadly a small reel of 8mm film can be.