‘Curiosity’, Conrad tells us in Lord Jim, ‘is the most obvious of sentiments.’ And if it was curiosity, restlessness, a dislike of George W Bush, or even boredom with his job as an English teacher in a Vermont prison that made Theo Padnos drop what he was doing and set out for Yemen, he should just tell us as much.

What he did instead – to the detriment of his otherwise excellently observed book – was pretend to become a Muslim. Were this just a ruse, the safest way – as Padnos correctly surmised – to penetrate the highly secretive world of international Islam, a Cairo–Damascus–Sana’a axis that