The film is adapted from Zhou Haohui's Douban suspense novel with a high score. The mysterious killer Darker, who calls himself the "judge", openly challenges the police and issues "death notices" one after another. Anyone who receives them will be brutally executed. In order to find out the truth, Huang Shaoping (played by Louis Koo), a witness of the explosion, the genius policeman Luo Fei (played by Julian Cheung), and the head of the special task force Han Hao (played by Francis Ng) all join the game. Who is Darker? The truth keeps turning around, and shocking secrets gradually surface...