Jang Chun Dong is a traffic officer who aspires to become a homicide detective. After being noticed by his superiors, Chun Dong is assigned to go undercover to infiltrate a gangster network headed by Yang Kwang Seob. Meanwhile, Lee Jung Dae, a member of Kwang Seob's gang, goes undercover himself by joining the police force. Jung Dae tries hard to gain favor with his squad leader and bureau director in an effort to expose Chun Dong's identity, but falls in love with a colleague, Cha Se Rin.