On the morning of the town fair Lily did not believe in elves. Lily's main concerns were fitting in with the other kids in her high school and her Dad's refusal to re-engage with life after her mother's death. All that changes when she and her friend Jackson fall into a mysterious, gaping hole on the outskirts of town. They find themselves in a cavernous underground world inhabited by a people who call themselves 'the Hidden.' While Lily and Jackson make friends with some Hidden their own age, it soon becomes clear that the leaders have no plans to allow them to return to the surface, where they might reveal the existence of the secret world of the Hidden. Lily suspects there is more to the Hidden's desire to keep her and her friend among them and that their 'fall' into the hole may have been no accident.