"None of that people should be spared, not even the babe in its cradle." With these chilling words, the Mongol warlord Genghis Khan declared his intention to destroy the Ismailis, one of the most intellectually and politically significant Muslim communities of medieval Islamdom. The massacres that followed convinced observers that this powerful voice of Shi'i Islam had been forever silenced. Little was heard of these people for centuries, until their recent and dramatic emergence from obscurity. Today they exist as a dynamic and thriving community established in over twenty-five...