Wow.
I have to say, even though I knew what was going to happen, I was as equally blown away when reading the ending, as I was the first time I saw the movie. Totally engrossing.
If you liked the movie- if you loved the movie- this novelization (written to promote the film's US release in 1978) is a must-read. By allowing us into Sgt. Howie's thoughts, the novel adds a significant layer of depth to the story. More importantly, the novel gives a very intricate and complete back-story on Sgt. Howie which makes him a much more sympathetic character than he was in the film.
Plot holes are explained or patched up, not to mention the fact that the story is much more intellectual than at first glance.
I see this story partially as a metaphor for the Sexual Revolution and Hippie movement of the 60's, and their conflict with the forces of conservatism arrayed against them. (My take is that the authors were saying that going too far to the extreme of either end of the cultural spectrum was a bad thing.) On a more superficial level, the story is a clever game in which a gallant hero is drawn into a situation well out of his control.
Really well done, and you can see what a labor of love this film was for its screenwriter and director. (Robin Hardy, the director, was the principal author of this novelization.)
Though this is billed as a horror movie/novel, it really transcends that genre in many ways. In this novel you get everything from theological debate, anthropology, history, feminism (how many horror novels name-drop Germaine Greer?), socioeconomics, ornithology, biology and folklore. It's also very "Scottish"- invoking Shakespeare, I would even go so far as nicknaming it "The Scottish Horror Movie".
I recently read David Pinner's "Ritual"- which inspired the movie, and have to say that Pinner's story doesn't have a patch on Hardy and Shaffer's very original creation.
Given that I saw the movie first, I can't recommend this book with any objectivity to someone who hasn't seen it. But, I thought this novel was fantastic, and I loved it.