A serious murder took place in Tang Dynasty’s capital city Chang'an. Ambassador of the Salo Kingdom was killed in a brothel. The case is investigated by Detective Dee and Hong Yun, but they are ambushed by the culprits, and Hong Yun's best friend is killed by a man named Tian Sha, who takes away the chrysalis of the evil Moth of Nirvana as a tribute. As a result of his unfavorable handling of the case, Dee was dismissed by Empress Wu Zetian and investigated. As a result, Yuan Feng, the commander of the Jingo Guard, summoned Di Renjie to the capital to investigate the case.