Xiao-Bai, a white snake demon, is sent on a mission to assassinate the Emperor's Taoist advisor, who has been killing snakes en masse in order to achieve immortality and curry the Emperor's favor. Xiao-Bai, however, is attacked by the advisor's lackeys before she can reach him and is subsequently defeated. Luckily, the demonic hairpin she was granted by the Snake Mother is able to save her life at the cost of her memories.

Xiao-Bai awakens in the Snake-catcher village, unaware that she is actually a demon or that she is surrounded by her sworn enemies. She meets Xu Xuan, the man who saved her, and is charmed by him. The two set out on a journey to discover who Xiao-Bai is, and learn the secret of her demonic hairpin. The pair is pursued by Xiao-Qing, Xiao-Bai's sister, who has sworn to the Snake Mother to retrieve Xiao-Bai within three days or die trying. As Taoists, demons, and humans collide, a tale of forbidden romance unfolds.