Tetrarch is a very interesting novel deserving addition to my Gnostic Catholic "Section 2" reading list ("Other books, principally fiction, of a generally suggestive and helpful kind"). It is a slightly didactic through-the-magic-door fantasy, like C.S. Lewis' Narnia, but definitely for adults. Instead of hokey Christian allegory, it offers reifications of William Blake's prophecies, Bohmian quantum mechanics, systems theory, transpersonal psychology, imaginary language, and encounters with historical personalities. The whole stew is pretty heady, and some prior familiarity with the prophetic works of Blake will help to avoid getting disoriented: the protagonists are supposed to be versed in them already, and the reader is given many allusions to them without further exposition.
Author Alex Comfort is, of course, best known for his book The Joy of Sex, and there is plenty of sex happening in Tetrarch, where the customary greeting is, "Have you loved well?" Narrator Edward and his partner Rosanna are preposterously enlightened in their sexuality: quite free of jealousy and compassionate about others' hang-ups. It's not porn; there's none of the sort of graphic detail that makes porn work, but the sexual vision--utopian and otherwise--is rather inspiring.
Thelemites may note the names Edward and Rosanna as corresponding closely to those of the scribe and seer of the Cairo Working. There is a lot of magick in this book, and learning among adepts is its principal preoccupation. It's nothing like Hogwarts, though, with the exception of the university of the Foursquare City described in the second part of the book--an institution in which the protagonists do not enroll. The central adepts of the story are initiated by pareunogenesis, a process of attainment by sexual contagion.
The "Tetrarch" of the title is Edward's steed in the visionary world, named after the champion Irish thoroughbred who beat all comers in 1913. Here, the Tetrarch is not a horse, however; it is rather a giant chalicotherium, from a family of ungulate mammals that prospered during the Eocene period. The exotic fauna of the Fourfold World are an interesting mix of the paleontological, the legendary, and the speculative. The Klars are a special treat: an idyllic race of Überbonobos.
The endpapers feature an attractive map of the Fourfold World, and appendices provide information on Losian language and religion. The latter is in a tabular form that reminds me of the correspondences chart appended to Gunther's Initiation in the Aeon of the Child. There is one evident error in the table, though: it needs initiated review before practical application!
I stumbled on this book entirely by accident in a used book store, and my 1980 first-edition copy is pretty worn, but it is attractive: a hardcover with a marbled dustjacket, its cover illustration showing Edward and Rosana on the Tetrarch, in a style that reminds me of paintings by the Scottish surrealist Fergus Hall. Although long out of print, it appears to be easy enough to find used online for reasonable sums.