I. Synopsis
In 1986, in the (fictional) city of Iltan in Gyeonggi Province: A young girl gets brutally murdered by an unknown person on a dark night. As the city is gripped by a succession of serial killings, a total of nine murders within a twelve-kilometer radius since 1993, the police conclude that a man they've nicknamed "Gap-dong" is behind the crimes. Detective Yang Cheol-gon (Sung Dong-il) is convinced that the actual killer is Ha Il-sik, a resident of the town who is intellectually challenged. His attempt to arrest the suspect fails as Ha commits suicide to prove his innocence. His death inspires his son Moo-yeom (Yoon Sang-hyun) to become a police officer to clear his father's name and restore his honor.
Seventeen years later, Moo-yeom is a police detective who spends his career chasing dead ends and helping juvenile delinquents. After the statute of limitations on the case expires, Moo-yeom becomes resigned to the belief that Gap-dong is dead. But then a series of incidents occur in the town that bears an eerie resemblance to Gap-dong's crimes. Cheol-gon, now a well-decorated officer, has recently transferred back to Iltan, and to his dismay, Moo-yeom joins his investigation team to catch Gap-dong once and for all.
