Synopsis: Veteran detective Seo Do-cheol and his team in the Violent Crimes Investigation Unit dedicate their lives to fighting crime, often at the expense of their personal lives.When a professor's death is linked to a series of previous murders, the entire nation is shaken by the emergence of a serial killer. As the detectives race to piece together clues, the killer taunts them by releasing a video online, revealing his next intended victim and plunging the country into further chaos.Amidst the turmoil, the unit enlists the rookie detective, Park Sun-woo, whose strong sense of justice quickly catches Do-cheol's attention.