As usual, in order to understand where the film is coming from we have to discuss the source material. Quick! To the library!
"The Dreams in the Witch House" is a short story by H. P. Lovecraft, part of the Cthulhu Mythos genre of horror fiction. Written in January/February 1932, it was first published in the July 1933 issue of Weird Tales.
Walter Gilman, a student of mathematics and folklore at Miskatonic University, takes a room in the Witch House, a house in Arkham thought to be accursed. The first part of the story is an account of the history of the house, which has once harbored Keziah Mason, an accused witch who disappeared mysteriously from a Salem jail in 1692. Gilman discovers that for the better part of two centuries many if not most of its occupants have died prematurely.
The dimensions of Gilman's room in the house are unusual, and seem to conform to a kind of unearthly geometry that Gilman theorizes can enable travel from one plane or dimension to another. In his dreams Gilman is taken to a city of Lovecraft's "Elder Things", and even brings back tangible evidence that he's actually been there. Several times his dreaming self encounters a bizarre "congeries of iridescent, prolately spheroidal bubbles", as well as a trapezoidal figure, both of which seem sapient.
Of much more direct concern, however, are Gilman's nightly dream sojourns with the old hag Keziah Mason and her rat-bodied, human-faced familiar Brown Jenkin, sojourns which he increasingly believes are actually happening in the real world. One night, Gilman dreams Keziah, Brown Jenkin, and the infamous "Black Man" force him to be an accomplice in the kidnapping of an infant. He awakes to find mud on his feet and news of the kidnapping in the newspaper.
On May Eve (Walpurgis Night), Gilman dreams that he thwarts Keziah from sacrificing the baby, only to have it killed by Brown Jenkin. Coming back to wakefulness in this plane, Gilman hears an unearthly cosmic sound that leaves him deaf. The next morning, Gilman is found dead in his room in the Witch House, a hole burrowed through his chest and his heart eaten out.
The landlord then abandons the house completely, and when it is finally demolished years later, a space between the walls is found filled with children's bones, a sacrificial knife, and a bowl made of some metal that scientists are unable to identify. A strange stone statuette of a star-headed "Elder Thing" is also found, and these items go on display in the Miskatonic University museum, where they continue to mystify scholars.
Curse of the Crimson Altar is a 1968 British horror film directed by Vernon Sewell and starring Christopher Lee, Boris Karloff, Barbara Steele and Mark Eden. The film was produced by Lewis M. Heyward for Tigon British Film Productions. The film was cut and released as The Crimson Cult in the United States. It is based (uncredited) on the short story "The Dreams in the Witch House" by H. P. Lovecraft. The house in the film is Grim's Dyke House in Harrow Weald, Middlesex, England, the allegedly haunted former home of William S. Gilbert; this film also featured the final appearance of horror heavyweight Boris Karloff.
Robert Manning (Mark Eden) goes in search of his brother who was last known to have visited the remote house of Craxted Lodge at Greymarsh. Arriving at night, he finds a party is in progress, and he is invited to stay by the niece of the owner of the house, Eve (Virginia Wetherell). But his sleep is restless and strange dreams of ritual sacrifice disturb him. Enquiring about his brother, he is assured by the house owner Morley (Christopher Lee) that the man is not here. But Manning’s suspicions are aroused further by his nightmarish hallucinations. When Manning learns from occult expert Professor Marshe (Boris Karloff) of a witchcraft cult based around the ancestral Lavinia Morley (Barbara Steele), the cult is uncovered. Craxted Lodge is burned to the ground, with the head of the cult being consumed in the flames.
When we say based on “The Dreams in the Witch House” what we really mean is someone read a blurb about that story and pieced together their own ideas because this is nothing like the source material. It feels more like your average Hammer film and less like the gothic horror it is supposed to be based on. Don’t get me wrong, it’s a great movie but may be a bit slow and dry for most people.