Thirteen-year-old Rio Kaiser's good intentions turn into life-threatening consequences when they land her and her friends in a savage, new world hidden beneath a mountain in rural Maine. When forced to confront her fears, Rio discovers she has a special gift which might save more lives than only her own. While caught in the middle of a war between two clans of a carnivorous creatures battling for supremacy, she must learn to harness her new ability, avoid capture by the creatures hunting her, and find a way home.