Mr. Socrates (2005)

Asking his imprisoned father for money, threatening a friend who became a murderer by mistake, stealing money from his friends; KU Dong-Hyuk (KIM Rae-won) is the worst scumbag you can ever imagine. Living a low-life existence like a street dog, until one day, Dong-hyuk gets kidnapped by a mysterious gang. Held captive for seemingly no reason, Dong-huk is "trained" by the gang in a secret and inhumane way. Dong-Hyuk tries to escape but fails, which makes the training more harsh and cruel than before. After finishing all the training, the gang orders Dong-hyuk to become a police detective as their secret connection. Once on the inside, he experiences divided loyalties.