In 1970, Angus Marlowe disappeared along with a strange occult artifact held in his family's possession for centuries—a black mirror. After entering a desolate Cedar Manor a few years ago, the investigators discovered a tome that revealed part of the Black Mirror's mystery—beyond its glass lay a gateway to another realm—but whatever happened to the mirror?

Now, a young woman's disappearance has led Susan Logan to discover its whereabouts. After investigating on her own, Susan becomes enraptured by the mirror's dark allure. Soon, the investigators encounter a woman who is not the Susan they know. Who is she? The baffling answer leads them to the Black Mirror's terrifying secret.