The young Dee Renjie arrives in the Imperial Capital, intent on becoming an officer of the law. Empress Wu, who has just ascended to the throne, has sent the fiery-haired Detective Yuchi to investigate a sea monster that stalks the city at night. By chance, both Dee and Yuchi fight off the creature when it attacks a ceremonial procession carrying the beautiful courtesan Yin to be sacrificed at a temple to appease the Gods. Suspicious of the stranger, Yuchi has Dee imprisoned. Dee escapes with the help of visiting doctor Shatuo and together they discover that the upper reaches of society, including the Emperor himself, are addicted to a poisonous tea produced by Yuan's famous teahouse but Yuan, who was romantically attached to Yin, has been missing for months.