When Mark's mom drives him and his sister Emily up to the front of the enormous Elsworth estate where his uncle works as caretaker, he immediately feels uneasy. His unease only grows. Carvings move when he's not looking, his little sister has a new imaginary friend who leaves when anyone approaches her, and he glimpses a strange boy in one of the mirrors who isn't there when he turns around. When his sister follows her imaginary friend into a place they'd been told never to go, Mark goes after her. They try to return only to find that the halls have changed behind them. The building is alive and it doesn't want to let them go. Can they get out? Even if they do, will they ever be the same?