Seo Do-cheol (Hwang Jung-min), a veteran detective who fights crimes day and night without taking care of his family, and the detectives of the Major Crime Investigation Unit.

One day, a professor’s death is linked to a series of previous murders, and the nation is abuzz about a serial killer. The detectives follow the clues and begin to investigate. But as if to mock them, the serial killer releases a trailer on the internet that reveals his next victim, shaking the nation once again.

The homicide squad assigns the youngest detective, Park Seon-woo (Jung Hae-in), who has a strong sense of justice that catches the eye of Seo Do-chul, and the case takes a new turn…