I Saw The Devil

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,

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 agent of the National Intelligence Service, is also present and vows to take revenge against the murderer. Soo-hyun learns of the four suspects from Squad Chief Jang and proceeds to privately torture and interrogate two of them. Upon searching the home of Kyung-chul, the third suspect, Soo-hyun finds Joo-yun's engagement ring, proving that Kyung-chul was the perpetrator.

A short time later, Kyung-chul brings a schoolgirl home and sexually assaults her. Soo-hyun beats him unconscious. Rather than killing Kyung-chul and being done with it, Soo-hyun decides to shove a GPS tracker down his throat, allowing him to see Kyung-chul's location in real time and to listen to his conversations. Waking up injured, Kyung-chul walks along the road and is offered a ride by a taxi already containing one passenger. Upon getting in, and correctly guessing that the driver and passenger are in fact two bandits intending to rob and murder him, one being Soo-hyun's unvisited fourth suspect, he strikes out preemptively and kills them both. Afterward, he finds the body of the real taxi-driver in the trunk. Kyung-chul throws out all three bodies, and drives to a small town where he sexually assaults a nurse. Soo-hyun arrives to subdue him and slashes his Achilles tendon before releasing him once more.

Kyung-chul visits the home of his friend Tae-joo, a murderer and cannibal. After explaining his situation to Tae-joo, the latter remarks that whoever is after him must be the relative of one of his victims. Kyung-chul consequently deduces Soo-hyun's identity after recalling Joo-yun's engagement ring, which Soo-hyun had put on before attacking him previously. Soo-hyun arrives and incapacitates both murderers along with Tae-joo's girlfriend Se-jung. The next day, Tae-joo and Se-jung, still unconscious, are arrested by the police and sent to the hospital. Soo-hyun's trusted subordinate arranges for Soo-hyun and Kyung-chul to evade the police and receive treatment for their wounds at a separate facility. The barely conscious Kyung-chul hears Soo-hyun and the subordinate talking about the transmitter.

Soo-hyun releases Kyung-chul again, but the latter outsmarts Soo-hyun, slashing the throat of a pharmacist while stealing laxatives which he uses to remove the transmitter, then plants it on a driver at a truck stop that he viciously beats. Soo-hyun enters Tae-joo's hospital room to question him, and learns too late that Kyung-chul is going after Squad Chief Jang and his other daughter Jang Se-yun. Angered, he breaks Tae-joo's jaw. Kyung-chul arrives at the house of Jang, and proceeds to brutally assault him with a dumbbell, then kill Jang Se-yun. Shortly after, Kyung-chul attempts to avoid Soo-hyun's revenge by surrendering to the police. However, Soo-hyun drives by and kidnaps Kyung-chul right in front of the police's eyes. Taking him to the earlier warehouse, Soo-hyun tortures him, places him under the makeshift guillotine, and leaves him holding a rope between his teeth to keep the blade from falling. Though he mocks Soo-hyun, Kyung-chul begins to panic when he learns that his son and elderly parents, whom he had abandoned some time ago, have arrived and are trying to visit him. As his family opens the door despite his muffled protests, it triggers another mechanism set up by Soo-hyun that drops the blade and brutally beheads Kyung-chul in front of his family. With Kyung-chul finally dead, Soo-hyun, who was listening through the transmitter some distance away, emotionally breaks down and begins crying in the street as he slowly walks away.