I Saw the Devil is a 2010 South Korean action thriller film directed by Kim Jee-woon and written by Park Hoon-jung. Starring Lee Byung-hun and Choi Min-sik, the film follows NIS agent Kim Soo-hyun (Lee), who embarks on a quest of revenge when his fiancée is brutally murdered by the psychopathic serial killer Jang Kyung-chul (Choi). I Saw the Devil made its premiere in the United States at the 2011 Sundance Film Festival and had a limited U.S theatrical release.

Plot

One night, a school-bus driver named Jang Kyung-chul encounters a pregnant woman named Jang Joo-yun and offers to fix her flat tire. After beating her unconscious, Kyung-chul dismembers Joo-yun at his home, and while doing so, Joo-yun's ring falls. Kyung-chul ignores it and scatters the body parts into a local stream. When a boy discovers one of Joo-yun's ears, the police arrive en masse to conduct a search, led by Section Chief Oh and Squad Chief Jang, Joo-yun's devastated father. The victim's fiancé, Kim Soo-hyun, an NIS officer is also present and vows to take revenge against the murderer.