Fierce and feared Zeus gang boss Jang Dong-su (Don LEE) gets involved in a fender bender on a rainy night and gets attacked without warning, ending up with several severe wounds. After fighting back, he barely kept his life but his reputation as a gang boss is damaged beyond repair. His only way to somehow get his image on track is to find his attacker and exact revenge. He decides to team up with Det. Jung Tae-seok (KIM Moo Yul), who believes that Jang’s attacker is none other than a serial killer. The two men pool their talents and resources at their fingertips to slowly find a serial killer simply known as “K”.