Wonderful story. Mackie the main character is actually a changeling. Most changelings do not survive into childhood but Mackie has an advantage. The family of the child he replaced have found it in their hearts to love him, especially his sister who has taken it on as her duty to protect him. He also has friends who support him. His parents and sister know he is not their child, and his best friend suspects. Mackie himself knows there is something wrong about him. Iron and steel cause him to suffer severe reactions and he cannot step onto hallowed ground. With his condition deteriorating he is approached by the Folk that live under the hill with a possible cure but is the cost too high? The world created in the Replacement is both strange and familiar and the tale is a marvelous twist on the fairy/folk tales of changelings. Not at all what one would expect. I loved the character of Mackie. Sympathetic and prickly at the same time.