When two cases of murder with identical crime pattern take place at a sports complex, homicide detectives Jo Kyung Yoon (Kim Kang Woo) and Park Eun Joo (Kim Min Sun) are called in to investigate the matter. They soon learn the history behind the two victims - both are believed to be military buddies who were charged for assault a decade ago. Suspecting revenge as a motive, the police zoom in on the victim of the assault, Lieutenant Lee Yun Seo. But the investigation reaches a dead-end, when they learn that their wanted man has been missing in action after suffering from fits of delirium and attempting suicide approximately ten years ago. Even the suspect's mentally stricken sister is clueless of her brother's whereabouts. While the pressure mounts on the police to crack the case, the killer strikes again - this time the victim is the third offender involved in the same assault case. But the more the police target Lieutenant Lee as their prime target, the more disturbed detective Jo becomes of his own past secret. Eventually, he launches his own investigation, catching his partner's suspecting eyes. As he delves deeper and deeper into the case, he uncovers further secrets that lead to an unspeakably shocking conclusion.