The Brotherhood of Satan is the novelization of a 1971 horror movie of no great critical note, and it certainly reads that way. While I haven’t seen the movie, I suspect that the book is very faithful to it, because it fails to offer any details that couldn’t be represented on film. (Author Jones was a member of the cast and assisted on the script.) The characters are cut-outs with little or no interiority. Despite that superficiality, some of the scenes are difficult to picture, particularly ones in the Satanists’ lair that involved passage “through” a fireplace. Supernatural occurrences get a gee-whiz treatment that makes them feel cheap.
As far as the Satanic conspiracy goes, it has a lot of liturgical action, which is what attracted my attention to the film/book in the first place. But the liturgy is decidedly uninformed and clumsy, with addresses to “Ye who penetrates the future” (ouch!) and “Satanacus.” The choice of an “ansate cross” for the principal insignia of the cultists is somewhat spoiled by the fact that the book cover and movie stills show a figure that is not really a crux ansata. The “Satanic” rites involve an unseemly level of self-abasement among the worshippers, and a practically Christian sense of penitence.
SPOILER: To its credit, the story ends with the triumph of the evil forces, with the hapless “protagonists” merely lulled into a grateful sense of having survived the episode, while their daughter has been spiritually possessed (presumably for life) by one of the creepy old cultists.