This South Korean film depicts a disturbing story of a serial rapist and murderer (played by Min-sik Choi, known for Oldboy) who targets the pregnant fiancée of a government agent (Byung-hun Lee, also appearing in A Bittersweet Life and The Good, The Bad, The Weird). What follows is the agent’s relentless pursuit of the killer, involving severe beatings, the placement of a tracking device, financial compensation, and eventual release. The intention appears to be inflicting prolonged suffering on the killer until his level of fear matches that of his victims, before ultimately ending his life. I Saw The Devil isn't perfect; clocking in at nearly two-and-a-half hours, it feels drawn out. The extreme violence risks becoming comical, particularly when the killer finds temporary shelter with a cannibalistic couple who are remarkably unfazed by the rape of their wife—apparently, one’s values can change when your partner consumes human flesh for amusement. Furthermore, the core idea of pushing this serial rapist/killer to experience intense terror like his victims doesn't quite work; Min-sik Choi’s portrayal suggests he is simply incapable of feeling fear. Consequently, the repeated capture and release cycle ultimately loses its purpose. Despite these issues, the film remains captivating, consistently tense for a good portion of its length, features outstanding performances from the actors, and delivers shocking violence and gore—though it's presented with careful control; the tone resembles Seven more than Saw. The cinematography is also remarkable. A serial killer movie centered on torture, set in snowy Korea, shouldn’t realistically have such vibrant colors, but each shot is visually striking.

Source on TMDB