Eighteen-year-old Gu Miyoung has a secret -- she's a gumiho, a nine-tailed fox who must consume the life force of men every full moon or die herself. Ever fearful of becoming more of a monster, Miyoung kills only when she has to, and even then, only those guilty of horrific crimes. When Miyoung finds Jihoon, a handsome human boy her age, being attacked by a goblin in the woods, she saves him, violating her mother's rules of survival and her own good judgement. But in the midst of the fight, Miyoung loses her fox bead -- her gumiho soul -- setting off a chain of events that ensnares both Jihoon and Miyoung in a deadly generations-old feud and forces Miyoung to choose between her immortal life and Jihoon's.