Speculative fiction is a broad umbrella category of narrative fiction referring to any fiction story that includes elements, settings and characters whose features are created out of imagination and speculation rather than based on attested reality and everyday life. That encompasses the genres of science fiction, fantasy, science fantasy, horror, alternative history, and magic realism.
This very unusual vampire story is not a fantasy but a psychological
study, albeit a fictional one. The novel is an expansion of a short
story which seems to have been first published in Alfred Hitchcock's