The story begins with the sons of the Hung-mo Emperor returning to the capital city as a show of filial piety to their father, who has fallen extremely ill. Secretly, the princes are harboring intentions to succeed the throne. As a result, chaos surrounds the kingdom, and a chain of conspiracies and schemes begin occurring in the city...
While pursuing a mission, Kamyi Wai agent Ngo Siu-fung loses his memory in an accident. As he begins to slowly piece back memories of his past, he realizes that he was once a vicious, unreasonable, and merciless Kamyi Wai commander. He decides to start anew and change his ways of style, but his colleagues are unable to see past Siu-fung's history of cruelty, and they continue to treat him unfairly. Fortunately for Siu-fung, he saves Chu Wan-man , grandson of the emperor, who has dressed himself in plain clothes to observe the commoners of the city. The two become good friends and Wan-man appoints Siu-fung as his personal bodyguard.
The emperor dies, his posthumous edict robbed, and the kingdom is left with no heir. The princes all desire the throne, leaving the kingdom unprotected from future attacks. Impatient, Wan-man orders Siu-fung to find the edict as soon as possible to stabilize the chaotic situation. The powerful and intelligent fourth prince Chu Tai , titled the Prince of Yin, also sends his most trusted adviser Ma Sam-bo to investigate the case. Fighting to retrieve the edict, Siu-fung and Sam-bo undergo a battle of wits and skill. They start an ambiguous friendship – though they see each other as equals, they are unable to work together because their loyalties lie elsewhere.
The edict is retrieved and Wan-man ascends to the throne, crowned as the Kin-man Emperor. Soon after his coronation, mysterious cases begin to occur around the kingdom. Someone with an ulterior motive is intentionally framing Tai of starting a coup. Though Tai is later proven to be innocent, Wan-man becomes really cautious of him. Aware that the new emperor has intentions in killing him, Tai raises an army to overthrow him. Under the slogan of "clearing the court and pacifying national disaster" (清君側、靖國難), Tai starts a coup d'état, that is later known to be called the Jingnan campaign .