This book is basically a discussion of the psychological makeup that characterises many religious leaders. Although Storr does not cover Joseph Smith, I have found that some aspects that he illuminates could be applied to Smith. I have often wondered whether Smith actually believed himself to be a prophet, or whether he was consciously aware of his deception. Storr points out that most gurus generally maintain both states of mind, to some degree. It is, paradoxically, the only thing which prevents them from descending into wholesale psychosis (although this particular brand of double-think did not appear to prevent Jim Jones or David Koresh from going over the edge).
He not only covers the psychology of gurus, but also touches on the psychology of belief, a subject that I am keenly interested in. Storr shows that belief in the irrational is not aberrant, but is in fact part of the normal human psychology. It takes great effort of will to break away from the seductive lure of belief, and such beliefs are no more susceptible to reason than psychotic delusions, or even the emotion of love. Why this should be so remains a mystery, and one that will probably only be solved once we learn substantially more about cognitive neuroscience.
I recommend this book highly.