Novelization of the 1975 horror movie The Devil's Rain - follows the film faithfully - It doesn't really clarify much except to explain that the people in The Devil's Rain are the souls of those who oppose Satan - so their empty bodies can then become vessels for Satan worshippers. The main idea is that 'it never rains in hell/staved off by Satan's spell' (so even though there's been a terrible thunderstorm, Stanville where the Satanic cult hole up is a complete dust bowl) because Satan's bounty is to stop it raining on his faithful. His enemies however..... are miniaturised, trapped in an urn in a perpetual rainstorm: 'Heaven's rain will burn Inside the Devil's Urn' - Yup its completely bonkers.
The film is like a Boschian nightmare and the book is just as bewildering and yet compelling. There are some differences clearly changed for budget - like the dad being out in the storm in a plane and the possessed having glowing eyes. The book doesn't really add much else other than some of the satanic chant/poems in full, but if you're a fan of the movie, it's a must have in the collection and it does have gorgeous turquoise sprayed edges.