In October 1986, a young woman is found raped and murdered in a ditch near a field. Soon after, another woman is found raped and murdered in a field. Local detective Park Doo-man, not having dealt with such a serious case before, is overwhelmed; key evidence is improperly collected, the police's investigative methods are suspect, and their forensic technology is near non-existent. Detective Seo Tae-yoon is sent from Seoul to assist them; their methods clash and he is unable to convince them they are dealing with a serial killer until his predictions of another murder come true. He realizes that the killer waits until a rainy night, and only kills women wearing red. A female police officer realizes that a local radio station is always requested to play a particular song during the nights the murders are committed.
While Seo investigates and tries to piece together the clues, Park and his men beat confessions out of a scarred mentally handicapped boy whom they threaten to kill, going so far as to make him dig his own grave, and a local man found masturbating at the scene of one crime. Seo clears both of those suspects and follows a trail of clues to a handsome factory worker who had only moved to the area a short time before the first murder. The detectives are unable to pin anything on him; when they realize that the handicapped boy witnessed one of the crimes and try to speak to him, they frighten him so badly that he runs in front of an oncoming train and is killed.
Finally, when yet another murder is committed and DNA evidence sent for processing in the United States comes back inconclusive, Seo's frustrations flow over and he snaps. He flies into a rage and roughs up the factory worker; only Park stops Seo from shooting the suspect.
In the end, the crimes remain unsolved. Visiting the crime scene years later in 2003, Park Doo-man, now a businessman, learns from a little girl that the scene had recently been visited by another, unknown man with a 'plain' face. The little girl had asked him why that man was looking at the ditch, and he told her that he was reminiscing about something he did there a long time ago.
Who tells Park Doo-man about the man with a 'plain' face?
little girl