When Hong Kong is rocked by multiple gruesome murders, the police forms a task force to investigate. Jun, once a brilliant detective who suffered a mental breakdown, begins his own investigation. Eventually, the police learn that the murder victims are all suspects of cold cases being rubbed out by a figure known as "The Sleuth". Now, Jun and a detective from the task force are on a race against time to beat the brutal killer at its own game.

As a frontline police officer, Li Chengyang faced oppression from all sides, framed by evil forces, and even his boss, the chief of public security, in order to prevent him from investigating.

A series based on the events in the reign of the Jiajing Emperor of the Ming dynasty.