I Saw the Devil (tt1588170) is a thrilling and intense revenge film from the director of Dark Secrets. Nearly banned in Korea due to its age restriction, the film follows a cat-and-mouse game between a psychopathic killer and a secret agent who takes pleasure in killing. Kyung-chul, the serial killer, commits horrifying murders with his diabolical intelligence, even targeting children. Despite the efforts of the police, he remains elusive. However, when the daughter of a retired police officer is brutally killed, her fiancé, undercover agent Dae-hoon, takes it upon himself to find the killer and deliver his own brand of punishment. The revenge is bound to be bloody, even if it means becoming a monster in the process...