This book contains an ethnographic study of al Muhajiroun, an outlawed radical jihadist group in London. Kenney seeks to explain how, despite intense police surveillance, the group survived, attracted adherents, and recruited fighters to join the war in Syria until the British government banned it in 2010. Ideological sympathy, ties of friendship, charismatic leaders, and youthful inexperience led people to join the group. Once there, they learned how to be activists by watching more experienced members, often imbibing even more dangerous ideologies along the way. Tight subgroups permitted the movement to deflect government pressure by frequently reconfiguring themselves and fostering ambiguity about their purposes. As they aged, some members left for more normal lives, while others turned to different, often more radical groups. These broad conclusions are hardly new, but some readers may be surprised by Kenney’s argument that such groups can allow young men to let off steam, thus containing, rather than promoting, violence. As the authorities stamp out these organizations, their disgruntled members may pose an even greater danger.