When his brother disappears, a man visits the remote country house where he was last seen. While the host seems outwardly friendly and his niece more demonstrably so, there's a feeling of menace in the air with the overhanging legend of Lavinia Morley, the Black Witch of Greymarsh.

Professor Monty Lafcado, haunted by the memory of his late mother, sets out to construct a mighty computer in his basement, much to the concern of his friend, Dr Pugh.