Inspired by the Islamic State, a wave of true believers traveled to Syria from Europe, America, and the Middle East, in numbers not seen since the Crusades. What compelled tens of thousands of men and women to leave comfortable lives to join a death cult in the desert? Graeme Wood uses character study, analysis, and embedded reporting to get an inside look at the Islamic State's apocalyptic vision. From the streets of Cairo to the mosques of London, Wood meets with supporters, recruiters, and scholars, asking them why they believe that killing and dying for this cause is the only path to Paradise, and in the process, uncovers the theology and emotional appeal of this resilient group.