korean movie, a soldier but want revenge

A man has only three and a half days and limited resources to discover why he was imprisoned in a nondescript room for 20 years without any explanation.

With no clue how he came to be imprisoned, drugged and tortured for 15 years, a desperate man seeks revenge on his captors.

Kyung-chul is a dangerous psychopath who kills for pleasure. Soo-hyeon, a top-secret agent, decides to track down the murderer himself. He promises himself that he will do everything in his power to take vengeance against the killer, even if it means that he must become a monster himself.