My impetus for reading this book largely came largely from my fondness for the author's superior The End of Science. The title of this book is a bit odd, since it doesn't make any particular case for the rationality of mysticism. The book is an easy read, but some of the gurus it discusses are not even interesting in their oddness. The author seems as fascinated by psychedelics as he does by spirituality, and the reader will likely come away having learned as much about the former as the latter.