A scientist develops a way to expand consciousness and unlock latent powers of perception, and the book spirals outward from there into telepathy, evolutionary possibility, psychic danger, and the suspicion that ordinary human awareness is only a narrow band of what the mind can do.

The Lovecraft comparison on the cover is not entirely nonsense, but Wilson is less interested in cosmic insignificance than in heightened consciousness tipping into terror.

It sits in a very particular lane: mid-century British intellectual pulp, where existentialism, occultism, horror, and speculative fiction all get thrown into the same beaker. Wilson has a loyal oddball readership, and this kind of period Panther paperback has proper object appeal alongside just simply being a great read. 

Panther paperback, 1974 edition; novel first published in 1969.