Cat Peters just transferred to Darkmont High and is already desperate to get out. When she hears that Grimoire, the private school nearby, is offering scholarships to the winners of a Halloween soccer match, Cat jumps at the chance. Her little sister, Sookie, and their bookworm neighbor, Jasper, try to tell her there's something ... just not right about the old school on the hill, and their worries are confirmed when they uncover a mystery about an entire soccer team that disappeared many years ago. Further investigation leads Cat to a book about ancient Celtic myth and fairy lore, and she soon realizes that there is something truly wicked at work inside the walls of Grimoire.