Cult leaders inspire intense loyalty among their followers, yet they strike outsiders as half mad. Why are there so many of them? And why do they and their ideas proliferate? In this controversial study of the thin divide that separates cult leaders from madness, evolutionary psychiatrists Anthony Stevens and John Price argue that what schizophrenics and prophets share in addition to similar genes is the capacity for sudden, radical changes of belief. Depending on the circumstances, this capacity may propel one group into psychiatric care and another into the creation of a new cult. Citing examples from Abraham and Moses to Shoko Asahara and David Koresh, Stevens and Price reveal the vital role that such schizotypal prophets play when human groups split and how their behaviour not only reveals an important evolutionary mechanism but also holds the key to one of psychiatry's persistent mysteries.