I Saw the Devil is a South Korean thriller film that explores and brutally deconstructs the theme of revenge. The movie is about Soo-hyun, a secret agent of the National Intelligence Service, whose fiancee is murdered by the infamous Kyung-chul, a serial killer that kidnaps and rapes his victims for pleasure. Having lost the person most dear to him, Soo-hyun makes it his life ambition to get his revenge, and that doesn't mean simply killing his fiancee's killer. He wants Kyung-chu to feel the same amount of pain and suffering as his fiancee did moments before her death. This kick-starts a heart-pounding game of cat and mouse, in which Soo-hyun stalks and consistently assaults Kyung-chu, before letting him go and restarting the whole process over again. As the film draws to a climax that results in a complete and total blood bath, the line between hero and villain is blurred into obscurity.
The film takes it upon itself to analyze common elements of the revenge genre. Delivering justice to a killer is all well and good, but what happens when the person dealing justice endangers the lives of innocents all for the sake of petite vengeance? The film is violent and unflinching in the face of gruesome murder, and the way it is shot reflects this. There are no jump cuts to show spare the viewer the awful sights they will witness. The camera is cold and deadpan as it slowly pans over the bodies of victims being shot and stabbed, just like how the two leading protagonists lifelessly preform terrible acts while having completely blank facial expressions.
The set-pieces moments of the film will leave the viewer thinking about what they had just witnessed months after they have seen it to begin with. It is both a disturbing and thought provoking piece of entertainment that will never leave the viewer bored for a second.