"I Saw the Devil" is a South Korean thriller film directed by Kim Ji-woon. The story follows a secret agent named Kim Soo-hyun, whose fiancée is brutally murdered by a serial killer named Jang Kyung-chul. Driven by grief and a desire for revenge, Kim embarks on a relentless pursuit to track down the killer. The film explores themes of vengeance, morality, and the psychological effects of violence. As Kim confronts Jang, the lines between hunter and hunted blur, leading to a tense and gripping narrative that challenges the viewer's perception of justice and retribution.