The film whose plot follows a man trying to discover why he was kidnapped and imprisoned for 20 years is Oldboy. This clue refers specifically to Spike Lee’s 2013 American film, in which Josh Brolin plays Joe Doucett, a man held captive without explanation before being suddenly released.
After his release, Joe searches for the people who imprisoned him and tries to understand their motive. His investigation leads through a private prison operation, hidden surveillance, revenge, and a mysterious adversary who gives him a deadline to uncover the truth. The film is a neo-noir action thriller with major psychological and mystery elements.
A frequent source of confusion is the acclaimed 2003 South Korean film Oldboy, directed by Park Chan-wook. It has a similar premise but imprisons its protagonist, Oh Dae-su, for 15 years rather than 20. The 2013 film is an official remake of that movie, and both ultimately trace their premise to the Japanese manga Old Boy by Garon Tsuchiya and Nobuaki Minegishi.