This book is the only Bio of the figure at the centre of modern Wicca, that is one Gerald Brosseau Gardner. I have seen in several places that it is almost certain that this book was written not by Jack Bracelin (who was Gardner's close associate, leaving Wicca later in life for Judaism if memory serves) but by the sufi author Idres Shah, a friend of Gardners. However I'm not sure if this is proven definitively anywhere.
The book itself seems to have been highly informed by Gardner and his unusual and adventurous life comes quite vividly through the writing. The current of spirituality and direct experience of these things runs through, from experiences with native Malay religions, Islam, freemasonry, spiritualism and the Kris daggers that Gardner became most strongly associated with. It also tracks his life through the more exotic fringes of the British empire, mostly in jungle terrain and his living as an enforcement agent and rubber plant cultivator.
Unfortunately for most prospective readers the latter of the two threads mentioned above tends to predominate along with his childhood circumstances, and there is not as much info on his involvement in the "witch cult" as one would perhaps like; however you can read about this elsewhere, notably in his own "the meaning of witchcraft" or Frederic Lamond's highly recommended "50 years of Wicca". It is however a very good read and enjoyable throughout.
For me, information such as this comes closer to the truer pulse of wicca than the many many witch guides that one can buy, heavy on spells but sadly low on spirituality. It is also a must read for the student of the origins of the modern resurgence of interest in Wicca.