During the Linde period of the Tang Dynasty, Emperor Gaozong of Tang (played by Sheng Jian) and Empress Wu Zetian (played by Carina Lau) forcefully sent a large army to an expedition, but the fleet was attacked in the sea and suffered a heavy blow. The incident shocked Luoyang, and the people of the capital city enthusiastically worshipped the Dragon King. The "Oiran" Yin Ruiji (played by Yang Ying) who confused everyone even attracted the covetousness of various forces. Di Renjie (played by Zhao Youting) was ordered by Empress Wu to investigate the case of the Dragon King, but happened to be involved in the kidnapping of Yin Ruiji. In the process of fighting with the robbers, Di Renjie encountered the Dali Temple Minister Yuchi Zhenjin (played by Feng Shaofeng), who was both an enemy and a friend, and was thrown into prison by the other party. The figure of the Dragon King reappeared in the case of Yin Ruiji, adding a cloud of doubt over Luoyang. In prison, Di Renjie won the trust of the Huihe medical worker Shatuo Zhong (played by Lin Gengxin) with meticulous reasoning, escaped from the prison and investigated the truth about the Dragon King. The two cases are complicated and intertwined, leading to a completely unknown direction...