The story revolves around Oh Dae-su (played by Choi Min-sik), a businessman who is kidnapped and held captive in a mysterious room for 15 years without any explanation. During his imprisonment, Oh Dae-su is subjected to physical and psychological torture, which fuels his desire for revenge against his captor. One day, Oh Dae-su manages to escape, and his first priority becomes finding his captor and exacting revenge.