"Lin Carter, rating it as the best non-fiction book of 1965 in the category of horror-fantasy books, called it "absolutely brilliant ... an utterly magnificent study of all phases of occultism, Theosophy, the Rosicrucians, spiritualism, alchemy, etc.--flawlessly researched, superbly erudite, beautifully written, and as devast[at]ingly keen-edged a hatchet-job as any since Voltaire invented the fine art of debunking."