All the world says that demons and evil spirits ought to be slain. But some demons harm people for the sake of revenge; some demons refuse to leave simply because they cannot let go of a person; and there are other demons who clearly wanted to save people, yet ultimately became the very appearance they hated most. Xi He is a demon catcher unlike any other. She does not ask whether one is human or demon, but only distinguishes between good and evil. When she encounters evil demons, she investigates karma first; when she encounters obsessions, she saves them if they can be saved. Behind one bizarre and uncanny demon disaster after another lie a bride forced into marriage, lamplight waiting for a returning traveler who never comes, and a vow that refuses to be let go of even across life and death. Yet, as one sealed past after another is uncovered, Xi He gradually discovers that hidden upon her own body is also a secret capable of shaking both the human and demon realms.