After the statute of limitations expires on a series of high-profile murders, a man named Lee Du-seok publishes an autobiography detailing the crimes he claims to have committed, along with descriptions of the victims and the locations where they were killed. His book becomes a bestseller, and he gains celebrity status, openly flaunting his supposed identity as the killer. The public is both fascinated and horrified by his brazen confession, while the detective who was in charge of the original investigation, Choi Hyeong-goo, is haunted by the fact that he could never catch the murderer and is skeptical of Du-seok's claims.

Surviving family members of the victims are outraged and devastated, as justice has eluded them. Among them is a mother whose daughter was one of the victims; she seeks out her own form of justice. Simultaneously, a mysterious person wearing a motorcycle helmet appears, attacking Lee Du-seok and leaving clues that suggest they have a personal vendetta linked to the murders. Detective Choi is torn between investigating Du-seok to find the truth behind his bold revelation and dealing with the violent vigilante that is targeting Du-seok, leading to a tense and dangerous pursuit of the truth.