The double story of Henry Day begins in 1949, when he is kidnapped at age seven by a band of wild childlike beings who live in an ancient, secret community in the forest. The changelings rename their captive Aniday and he becomes, like them, unaging and stuck in time. They leave one of their own to take his place, an imposter who must try–with varying success–to hide his true identity from the Day family. As the changeling Henry grows up, he is haunted by glimpses of his lost double and by vague memories of his own childhood a century earlier. Narrated in turns by Henry and Aniday, follows them as their lives converge, driven by their obsessive search for who they were before they changed places in the world.