Two decades ago, Lee Dong Sik (Shin Ha-kyun) was one of the celebrated detectives in the police force. He was on the up and up to become a law enforcement ace. However, a mysterious serial murder turned everything upside down – both in the police force and on the home front.
He has since gone from hero to zero, having to manage the menial tasks at the Manyang Police Substation. Unfortunately, the past keeps haunting him. A young rising-star detective from a high-profile background named Han Joo Won (Yeo Jin-goo) is transferred to the same station he was in to oversee Lee Dong Sik.
Han Joo Won’s father is in the running to win a bid to become the next national police chief. However, it appears this young rookie also has secrets he’d rather not share. When a series of copycat murders occured reminiscent of the same murders some 20 years ago, the two men are forced into an alliance that forced them to face a conspiracy that may involve high-status public officials.