Aleister Crowley is best known today as a founding father of modern occultism. His wide, hypnotic eyes peer at us from the cover of The Beatles "Sgt. Pepper s Lonely Hearts Club Band," and his influence can be found everywhere in popular culture.

Crowley, also known as the Great Beast, has been the subject of several biographies, some painting him as a misunderstood genius, others as a manipulative charlatan. None of them have looked seriously at his career as an agent of British Intelligence.

Using documents gleaned from British, American, French, and Italian archives, "Secret Agent...