The Attic

After her family moves, Emma becomes withdrawn and agoraphobic, terrorized by a girl in the attic who is her identical twin. Suspecting it's the ghost of her deceased sister Beth, she believes her parents are using witchcraft to bring her back. Her paranoia spirals into a violent tragedy where she kills her family. The shocking conclusion reveals her twin and a helpful detective were figments of her imagination, a psychotic break triggered by the haunted house itself.