As others have already said, this is a book of two halves. The early part explains how Al Qaeda came to be, outlining the opinions and beliefs Osama Bin Laden and others adopted. About half-way through the book changes and focuses more on the path to 9/11, detailing how the plot came to be and how everything came together on that fateful day.
Meticulously researched and brilliantly written this reads like a thriller, such is its gripping nature, and yet unlike any thriller it is truly terrifying as you know it is entirely true, and the manner in which the intelligence services in the US refused to cooperate is simply staggering - with a little more willingness to share information the whole plan could have been thwarted.
A truly excellent book. Only one problem though: the pictures weren't in my copy. At the back of the book there is an index of photographs used in the book, and yet there were none in my copy. Maybe I just bought a dud.