According to ancient lore, if a human freely offers their heart to a demon, that monster can become mortal, experiencing the true pains and passions of existence. This is the ultimate triumph of the underworld. Xiaowei (Xun Zhou), a millennia-old fox spirit, is freed from her frozen prison and transforms into a dangerous seductress, consuming living hearts to keep her beautiful as she searches for her chance to become human. Meanwhile, Princess Jing (Wei Zhao) hiding her marred beauty behind a golden mask, flees an unknown threat to her kingdom by pursuing the only man she ever loved: the guard who was unable to protect her, so many years ago. A twist of fate brings Princess Jing and Xiaowei together, and a slow game of wits, deceit, and seduction begins for the princess' very own heart.