Kyung-chul is a dangerous psychopath who kills for pleasure. Soo-hyeon, a top-secret agent, decides to track down the murderer himself. He promises himself that he will do everything in his power to take vengeance against the killer, even if it means that he must become a monster himself.

Never flinching during its descent into depravity, I Saw the Devil is a pulverizing thriller that will give bloody satisfaction to audiences who like their revenge served with fiery rage.