The Late Breakfasters - Robert Aickman (Gollancz 1964)
"I dedicate this book to Herbert van Thal, Magician."
The only novel published by Aickman during his lifetime (The Model was published posthumously, and apparently there's an unpublished novel in manuscript), you'd probably need a fairly liberal interpretation of the word to classify this as a horror novel, although it does have at least one ghost amongst the supporting characters, and there are enough unexplained disappearances and ambiguous conversations to mark this out as his work. The closest point of comparison is probably Evelyn Waugh's 1930s novels, though with substantially fewer jokes about black people being cannibals, which is definitely progress of a kind.
“But the nightmare had each time seized and penetrated her whole body and mind; it was as if she had been twisted into another identity, mysterious and horrible, which, when she returned, there could be no question of remembering since the two beings had no capacity for memory in common. She shuddered to reflect that this second identity, totally unreachable lay always behind her face and beneath her thoughts.”
“In the sunshine before the porte-cochère, a strange figure sat upon the stones of the drive working. It appeared to be a dwarf. It had very long arms (like a cuttlefish, Griselda thought), very long black hair (somewhat like horsehair), and a completely yellow face. Its ears were pointed, with strands of stiff black hair rising from the top of them. It wore black clothes. Very industriously, despite the great heat, the figure was polishing a large black piece of wood.”