The house on Fleming's Island had been left to rot. Ever since a strange and unexplained death soon after it was built, and plagued with troubling rumours about what lurked there, it remained empty and ignored for decades until the Cult moved in. As twenty people filled its many rooms, the eerie building seemed to be getting a new lease of life.

But now it is empty again. The cult found something in its corridors... and then vanished.

Trapped on the island one dark night, the Doctor, Tegan, Nyssa and Adric look into the building's mysteries, its stories of madness and death. Their only chance is to understand what terrible thing has been disturbed here... before it consumes them utterly.