When his brother disappears, Robert Manning pays a visit to the remote country house he was last heard from. While his host is outwardly welcoming - and his niece more demonstrably so - Manning detects a feeling of menace in the air with the legend of Lavinia Morley, Black Witch of Greymarsh, hanging over everything.

Robert Manning, an antique dealer, travels to Greymarsh Lodge in search of his brother who failed to return from a buying trip. Morley, the owner of the lodge, tells Robert that his brother never stayed there, but Robert is suspicious since he received a letter from the lodge only 10 days ago. His first night at Greymarsh is Witch's Night, a local holiday which commemorates the burning of Lavinia, a witch who once inhabited the lodge. Robert is warned by Elder, the butler, to stay away, but Robert is intrigued by Morley's niece Eve and decides to stay. On two successive nights Robert is summoned in his dreams by his brother who takes him to Lavinia's chamber; Lavinia tries to force him to sign a confession, and on the second night, he awakens with a knife wound in his arm. The next day, Professor Marsh, an expert on the occult, informs Robert that he is a descendant of the principal accuser at Lavinia's trial and that she swore revenge on the Manning bloodline. Robert and Eve set out to locate the witch's chamber and find the body of the butler in a secret passageway. Morley, who believes that he is a warlock with the task of avenging his dead ancestor, traps them in the chamber and is about to kill them when Professor Marsh and the police arrive. Before Morley can be apprehended, he sets fire to Greymarsh and dies in the flames.