When eight-year-old Abbie Brown discovers a quiet pool of water while wandering through the woods behind her Oregon home, she wades out into it and discovers she's not alone. A wild-haired boy in green stares at her from the other side of the water. Mesmerized, Abbie reaches down to him, and is yanked underwater.

She emerges on the other side as an unwelcome visitor to the Otherworld, the land of the Fae, with only the boy Foster to guide her. Back in Oregon, a changeling lookalike has taken her place, bonding with her mother while her father, hiding a secret of his own, views the "girl" with suspicion.

In the courts of the Fae a truce has long been in place between Winter and Summer. What havoc might a human child wreak in the careful machinations of beings older than time? And to what lengths will Abbie's father go to get her back?