On a summer night, Henry Day runs away from home and hides in a hollow tree. There he is taken by the changelings - an unaging tribe of wild children who live in darkness and in secret. They spirit him away, name him Aniday, and make him one of their own. Stuck forever as a child, Aniday grows in spirit, struggling to remember the life and family he left behind. He also seeks to understand and fit in this shadow land, as modern life encroaches upon both myth and nature. In his place, the changelings leave a double, a boy who steals Henry’s life in the world. This new Henry Day must adjust to a modern culture while hiding his true identity from the Day family. But he can’t hide his extraordinary talent for the piano (a skill the true Henry never displayed), and his dazzling performances prompt his father to suspect that the son he has raised is an imposter. As he ages the new Henry Day becomes haunted by vague but persistent memories of life in another time and place, of a German piano teacher and his prodigy. Of a time when he, too, had been a stolen child. Both Henry and Aniday obsessively search for who they once were before they changed places in the world.