Jihadist terrorism is widely seen as a threat apart, uniquely barbaric and dangerous. Underpinning the general fascination with the phenomenon are some well-worn assumptions: that its violent savagery is the product of religious fanaticism; that Western countries are the prime target; that terrorism, once it takes root, can rarely be eradicated. The image of Islamist violence as primitive and exotic has been enthusiastically fostered over recent years by both those who recruit individuals to terrorism and those who write about it for a Western audience.

As this compelling book demonstrates, the truth is more complicated and more interesting. Although jihadist terrorism is by its nature ideological, more people come to it through criminal, family and friendship networks than through the study of holy texts. The death toll from terrorism in the West since 9/11 has been far smaller than was generally predicted, even in countries whose security services are less effective than our own. Released terrorists are markedly less likely to reoffend than other ex-prisoners.

Mark Townsend’s book provides a narrative route to the heart of what we may come to think of as the Syrian phase in modern jihadist terrorism. He tells how three brothers, Amer, Abdullah and Jaffar Deghayes, and two of their friends, their families rooted in Libya, Sierra Leone and Bangladesh,