The Gangster, The Cop, The Devil

The Gangster, The Cop, The Devil is a South Korean crime thriller from the renowned Cannes Film Festival, starring legendary Train To Busan actor Don Lee. Fierce gang boss Jang Dong-su (Don Lee) is violently attacked after a fender bender on a rainy night. After fighting back, he barely escapes.
However, his reputation as a feared leader is damaged beyond repair. The only way to restore his image is to find his attacker and exact revenge. Jang teams up with Detective Jung Tae-seok (Kim Moo-yul) to find the assailant but soon discovers the attacker is a serial killer.
With no support from the police department, Detective Jung is forced to use gang boss Jang's resources to track down the killer. The two men must work together to find a man known as "K."