Seven-year-old Ellen wants nothing more than to play outside like a normal child, but an illness that has afflicted her since birth prevents her from doing so. Not wanting to burden her parents, she remains isolated in her room, but soon tragedy strikes and her parents abandon her. With nowhere to return to, Ellen meets a strange cat that makes a tempting offer she cannot refuse—a safe place to live in exchange for becoming a witch. To her delight, when she awakens in her new home, she is no longer afflicted with sickness; however, she soon discovers that leaving the house is not an option—one step outside and she will revert back to her former sickly self.

Ellen is unhappy being bound to the house, but things look up when the cat promises to teach her a spell that will be able to heal her completely in return for feeding him souls. Despite her wish being childish and forgivable, Ellen's quest for a healed body will kill many, and take far more from them than just their lives.