The narrative centers on NIS agent Kim Soo-hyun (Lee Byung-hun), whose world is shattered when his pregnant fiancée, Joo-yeon, is brutally murdered by a psychopathic serial killer, Jang Kyung-chul (Choi Min-sik).
The film's primary focus is the moral and psychological cost of vengeance. I Saw the Devil (2010) - IMDb i+saw+the+devil+mongol+heleer
Unlike traditional revenge films where the protagonist hunts the killer for a final confrontation, Soo-hyun identifies Kyung-chul early on. Instead of handing him over to the police, he begins a sadistic game of "catch-and-release". He beats the killer to near death, implants a GPS tracking device in him, and then sets him free—only to hunt him down again whenever Kyung-chul attempts to commit another crime. The narrative centers on NIS agent Kim Soo-hyun
