Inspectors CHO Kyung yoon and PARK Eun joo have been an inseparable duo ever since their police academy days. One day, the two inspectors take on the case of a young rich sports center owner, violently stabbed to death. The only clue to the case is a piece of body hair with AB blood type found at the scene. The two inspectors identify a swimming instructor as a major suspect to the case, but he later gets brutally murdered in the same way. It is later revealed that the two victims and a third party were once in the same army and committed a disgraceful act together. The police see the murders as a serial murder case in revenge for the victim at the time, 'LEE'Yoon suh . But as the murderers identity slowly unfolds, inspector Kyung yoon comes across another shocking mystery.

Inspectors CHO Kyung yoon and PARK Eun joo have been an inseparable duo ever since their police academy days. One day, the two inspectors take on the case of a young rich sports center owner, violently stabbed to death. The only clue to the case is a piece of body hair with AB blood type found at the scene. The two inspectors identify a swimming instructor as a major suspect to the case, but he later gets brutally murdered in the same way. It is later revealed that the two victims and a third party were once in the same army and committed a disgraceful act together. The police see the murders as a serial murder case in revenge for the victim at the time, 'LEE'Yoon suh . But as the murderers identity slowly unfolds, inspector Kyung yoon comes across another shocking mystery. [ Contract ]