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Jang Choon-dong is a traffic officer who aspires to become a homicide detective. He is assigned to go undercover to infiltrate a gangster network. Meanwhile, Lee Joong-dae, a member of Kwang-seob's gang, goes undercover himself by joining the police force....

The story takes place in a Southeast Asian country. Many years ago, a cold case that remains unsolved to this day involved Song Yang as the sole survivor. He became the only witness to the case, while his grandfather, Song Zhao Lin, was the victim. For over a decade, Song Yang has been searching for the whereabouts of the killer.