Wrapping up the first 2 of the trilogy (The Tower, The Delta), a balance, of sorts, has been reached among humans, spiders, and beetles. Obviously, humans have some catching up to do, having been enslaved for many generations. We learn more about what led to the "downfall" of humans and the domination of the spiders and beetles. Actually, there is much to learn from the hubris of humans which led to their fall. The story of the rise of the spiders and beetles is fascinating in and of itself. Then again, for those who have the eyes to see, so to speak, the 3 books of this trilogy are interesting/insightful for the ways in which other conscious species may view humans.
All that aside, our hero, Niall, now seen as godlike, begins to deal with the aftermath from generations of human enslavement and selective breeding by the spiders. This newly established stasis creates room to discover a mysterious, potent, other presence i.e. the Magician. In the process we are treated to, if you will, a deepening of awareness into the inner world potentials of humans by learning more about the inner world of the spiders' telepathic connection as seen/discovered thru the experiences and mind of Niall.
While this book reads much like a murder mystery thru the introduction of the malefic character known as the Magician...quite the fellow that one...it's a tremendous set up for the 4th and final book, The Shadowland. Make no mistake, Colin Wilson, a man of very high intellect, began his career as a philosophical intellectual writer with his 1st book, The Outsider (non-fiction), at the age of 24. Later, he wrote fiction concerning the occult, metaphysics, science fiction, fantasy etc.. His books are expansive, yet simple; rich, not obscure, and will be appreciated on whatever level of awareness they are experienced by the reader...a healing tonic for awakening/restoring the imaginative and creative faculties.