Maajid Nawaz spent his teenage years listening to American hip-hop and learning about the radical Islamist movement spreading throughout Europe and Asia in the 1980s and 90s. At 16, he was already a ranking member in Hizb ut-Tahrir, a London-based Islamist group. He quickly rose through the ranks to become a top recruiter, a charismatic spokesman for the cause of uniting Islam's political power across the world. Nawaz was setting up satellite groups in Pakistan, Denmark, and Egypt when he was rounded up in the aftermath of 9/11 along with many other radical Muslims. He was sent to an Egyptian prison where he was, fortuitously, jailed along with the assassins of Egyptian President Anwar Sadat. The 20 years in prison had changed the assassins' views on Islam and violence; Maajid went into prison preaching to them about the Islamist cause, but the lessons ended up going the other way. He came out of prison four years later completely changed, convinced that his entire belief...