Dragon Nine, an imperial detective, is on his way back after concluding the case of the Thief Ghost. He encounters "Sword Saint" Yeh, who asks him to tell "Sword Deity" Simon to meet him for a duel on the night of the full moon at the highest rooftop of the Forbidden Palace. News of the upcoming duel between the two greatest swordsmen spread like wildfire and attract much attention, with people starting to place bets on the final outcome. The Emperor sends Dragon Nine and Princess Phoenix to stop the duel from taking place and investigate whether it is a mask for any sinister plots.