Female detective Li Yiyue went to the northwest to investigate a case and met Tong Ling, the third prince of Beihai Dragon, and fell in love with each other, but was framed by the inner demon of the immortal, Nightmare, and became enemies. In order to save their lives, Yue Lao erased their memories and the two separated from then on. Three years later, Li Yiyue and Tong Ling met unexpectedly, and they fell in love with each other again by mistake, and joined hands to eliminate Nightmare and save the world.