"I Saw the Devil" is a 2010 South Korean thriller directed by Kim Jee-woon and written by Park Hoon-jung. The movie stars Lee Byung-hun as NIS agent Kim Soo-hyeon and Choi Min-sik as serial killer Kyung-chul.
The movie begins with Kyung-chul driving down a deserted road in his van. He sees a car stranded on the side of the road and decides to stop and offer help. The driver of the car is Joo-yeon, played by Oh San-ha, a young woman who is on her way home to her fiancé, Kim Soo-hyeon. Kyung-chul brutally murders Joo-yeon and disposes of her body.
Kim Soo-hyeon becomes obsessed with finding Joo-yeon's killer and begins investigating her death. He is able to obtain CCTV footage that shows Kyung-chul's van at the scene of the crime. Kim Soo-hyeon uses this footage to track down Kyung-chul and confronts him in a restroom. He beats Kyung-chul unconscious and takes him to an abandoned factory.
Kim Soo-hyeon tortures Kyung-chul and releases him, intending to track him down again and torture him some more. He follows Kyung-chul to a brothel and watches as he picks up another victim. Kim Soo-hyeon intervenes and saves the woman, but Kyung-chul escapes.
Kim Soo-hyeon continues to track down Kyung-chul and torture him each time he catches him. He is driven by a desire for revenge and a need to inflict the same pain on Kyung-chul that he inflicted on Joo-yeon. Kyung-chul, in turn, becomes increasingly sadistic, targeting people close to Kim Soo-hyeon in order to draw him out.
The movie escalates in violence and tension as the two men engage in a game of cat and mouse, with each trying to outdo the other in their acts of brutality. The final confrontation between Kim Soo-hyeon and Kyung-chul is bloody and brutal, with both men sustaining serious injuries.
In the end, Kim Soo-hyeon is left alone, haunted by the violence he has inflicted and the toll it has taken on him. Kyung-chul, however, remains unrepentant, even in the face of death.
The movie is notable for its unflinching portrayal of violence and its exploration of revenge and the toll it takes on those who seek it. The performances of Lee Byung-hun and Choi Min-sik are particularly noteworthy, with both actors delivering powerful and convincing performances that drive the movie forward.
Overall, "I Saw the Devil" is a gripping and intense movie that will leave viewers on the edge of their seats. It is not for the faint of heart, however, as it contains graphic violence and disturbing themes.