The story revolves around Oh Dae-Su (played by Choi Min-sik), a businessman who finds himself kidnapped and imprisoned in a mysterious room. With no recollection of how he got there, Oh Dae-Su soon discovers that he has been held captive for 15 years, with no apparent motive or endgame in sight. Driven by a desire for revenge and a need to uncover the truth, Oh Dae-Su begins to plot his escape, setting in motion a chain of events that will change his life forever.