The story of a man named Yook Dong-sik who coincidentally witnesses a murder and picks up the killer's diary. While fleeing the scene, he gets into a car accident causes him to lose his memory. Due to the diary in his possession, he mistakenly believes that he is a psychopathic serial killer.
Yook Dong Sik works at a brokerage company. He is a pushover and a fool too naïve and kind-hearted for his own good. Dong Sik is at a point in his life where enough is enough and goes to end his life. However, the place he chose to end it all was a place where a murder was about to happen. As he flees in fear, he gets into an accident, and the following day, doesn’t remember a thing in his past. The only clue he has about himself is a red diary he unknowingly took. The journal contains details of all heinous killings of a psychopathic serial killer. Being an innate fool, he mistakenly begins to believe that he is a psychopathic serial killer, and the world he once knew changes drastically.