September 11, 2001: Abbas watches live on Siberian television the tragedy taking place thirteen time zones away. His instinct tells him this monumental act of terrorism can only be the work of Muslim jihadists.

A year later, confronted with a giant cross erected on the ruins of the World Trade Centre, he asks: "does one form of religious intolerance lead to another?", and embarks on a seven year project completed in the book "In Whose Name?"

Driven by a desire to understand how the umma, the polity of Muslims throughout the world, let violent jihadism develop in its midst, he travels through...