Oh Dae-su is an ordinary Seoul businessman with a wife and little daughter who, after a drunken night on the town, is locked up in a strange, private prison for 15 years. No one will tell him why he's there and who his jailer is, but he is kept in reasonably comfortable quarters and has a TV to keep him company. Watching TV though, he discovers he has been framed for his wife's murder and realizes that, during one of the occasions in which he's knocked out by gas, someone has drawn blood from him and left it at the scene of the crime. The imprisonment lasts for 15 years until one day Dae-su finds himself unexpectedly deposited on a grass-covered high-rise rooftop. He's determined to discover the mysterious enemy who had him locked up. While he's eating in a Japanese restaurant, his cell phone rings and a voice dares him to figure out why he was imprisoned.