The movie I Saw the Devil is a South Korean thriller directed by Kim Jee-woon and stars Lee Byung-hun as Soo-hyun and Choi Min-sik as Kyung-chul. The film is known for its graphic violence and disturbing nature, as it explores the themes of revenge, morality and the dark side of humanity.
After Joo-yeon's murder, Soo-hyun sets out to avenge her death by embarking on a mission to track down her killer. He brutally beats Kyung-chul and inserts a GPS tracker inside his body, allowing him to torture him repeatedly without killing him, in order to prolong his suffering. Soo-hyun's pursuit of Kyung-chul becomes an obsession, leading him down a path of darkness and destruction.
As the film progresses, Soo-hyun's descent into madness becomes more apparent, as he becomes more brutal and sadistic in his attempts to extract revenge. Meanwhile, Kyung-chul is revealed to be an equally depraved and sadistic killer, who revels in his victims' pain and suffering.
The film's climax sees Soo-hyun confronting Kyung-chul for a final showdown, where his thirst for vengeance culminates in a shocking and graphic fight scene. The ending is left open to interpretation, with the audience left to ponder the moral implications of the characters' actions.
I Saw the Devil is hailed by critics for its exceptional cinematography, pacing, and acting performances. It is also considered one of the most disturbing and violent movies ever made, making it suitable only for mature audiences.