For hundreds of years Westerners have been fascinated by stories of the Assassins, their mysterious leader and their remote mountain stronghold at Alamut in Northern Iran. The legends first emerged in the 12th and 13th centuries, when Crusaders in Syria came into contact with the Nazari Isma'ilis, one of the communities of Shi'ite Islam who, at the behest of their leader Hassan Sabaa (mythologized as the "Old Man of the Mountain"), engaged in dangerous...