I will say this for my Essential Horror book, it is all over the damn place in terms of quality. From real stinkers like The Maze to great films like The Picture of Dorian Gray, you really get a feel for the full history of horror by following their suggestions. Luckily, Curse of the Demon (aka Night of the Demon) lands way closer to the high quality mark than low. Directed by Jacques Tournier, who directed Cat People, this is an older horror film that captures just the right shade of ambiguity...sort of.
The film opens with an attack by the titular demon right away. The effects are pretty impressive for what was surely a low budget film. Apparently, Tournier never wanted the Demon to appear onscreen, thus making a case that the horror was all due to the power of suggestion. But the studio said, "screw that noise" and built a demon suit for someone to wear. He thought it ruined the ambiguous nature of his movie but I disagree. Since the demon looks just like the one portrayed in the old wood carvings the characters review at the beginning of the film, I think the idea of suggestion holds up.
Anyway, the story is that Dana Andrews is a psychologist flying to England for a symposium on parapsychology. The poor schmuck who dies in the opening sequence was a colleague who planned to expose a Devil worshipper named Karswell at the conference. Andrews runs afoul of Karswell almost immediately as well as the hot daughter of his dead colleague. Together, he and the daughter investigate whether or not Karswell can really summon a demon before they get to October 28th (the day Karswell says Andrews will be killed). You have the ticking clock of The Ring along with the psychological ambiguity of Cat People. One sequence, at a seance, is so ridiculous that you can't help but believe it is fake just like Andrews (he is definitely the Scully of the duo).
The ending is very satisfying and nerve-wracking. Along with Andrews attempt to break into Karswell's home, the movie is full of memorable sequences (and one useless trip to Stone Henge). For fans of psychological horror, I highly recommend this one.