Oh Dae-su (Choi Min-sik) is a husband and father whose reputation for womanizing is well known. One day, for reasons he doesn't understand, Oh Dae-su finds himself locked up in a prison cell, with no idea of what his crime was or whom his jailers may be. With a small television as his only link to the outside world and a daily ration of fried dumplings as his only sustenance, Oh Dae-su struggles to keep his mind and body intact, but when he learns through a news report that his wife has been killed, he begins a long and difficult project of digging an escape tunnel with a pair of chopsticks.
Before he can finish -- and after 15 years behind bars -- Oh Dae-su is released, with as little explanation as when he was locked up, and he's soon given a wad of money and a cellular phone by a bum on the street. Emotionally stunted but physically strong after 15 years in jail, Oh Dae-su struggles to unravel the secret of who is responsible for locking him up, what happened to his wife and daughter, and how to best get revenge against his captors.