唐朝麟德年间，唐高宗与武则天强硬派出大军远征，谁知舰队在大海中遇袭，遭到重挫。该事件震惊洛阳，都城百姓狂热祭拜龙王，缭乱众生的“花魁”银睿姬更惹来各方势力觊觎。狄仁杰奉武后之命调查龙王一案，偏巧卷入绑架银睿姬的案件之中。在与劫匪搏杀过程中，狄仁杰遭遇亦敌亦友的大理寺卿尉迟真金，遂被对方投入大牢。银睿姬一案内龙王身影再现，使洛阳上空更添一道疑云。狱中狄仁杰凭借缜密推理博取回纥医工沙陀忠的信任，逃出大牢的同时，查明龙王的真相。两起案件错综复杂，相互纠缠，引向全然未知的方向。 During the reign of Emperor Gaozong of Tang, the emperor and empress dispatch a huge naval force to quench a rebellion, but the fleet is attacked halfway and suffers huge losses. Rumor has it that it’s the doing of a “Sea Dragon” and to placate it, a young courtesan named Yin Ruiji is selected by the citizens as an offering. The royal court entrusts Di Renjie to investigate the case, and things get even more complicated when a mysterious group of people try to kidnap Yin Ruiji. During his investigation, Di Renjie is thrown into jail by Yuchi Zhenjin, the Minister of the Ministry of Justice, who believes he’s an enemy. The capital city, Luoyang, is seized by fear as people believe a monster is at large. Di Renjie manages to win the trust of Shatuo Zhong, a prison doctor, who later helps him escape. Once he’s freed, Di Renjie embarks on a journey to uncover the truth, but things seem to be more puzzling than he had originally expected.