In the summer of 1978, Musa al Sadr, the spiritual leader of the Muslim Shia sect in Lebanon, disappeared mysteriously while on a visit to Libya. As in the Shia myth of the "Hidden Imam," this modern-day Imam left his followers upholding his legacy and awaiting his return. Considered an outsider when he had arrived in Lebanon in 1959 from his native Iran, he gradually assumed the role of charismatic mullah, and was instrumental in transforming...