If you're interested in Marks it's definitely worth reading. Some of it gets quite geeky on the details of the British secret service in WWII and specifically coding. However, even if you're not reading with a particular interest in those things, there is a lot of human interest.

I read it for a piece I just recently finished in draft--another part of the Novel. Since I can definitely get my geek on about the subject matter I may not be the most objective person to recommend it. It's got enough about some of the major players in Marks' section to have been required reading in my case. His writing style is very personal and more than a little breathless, but it does give you a real sense of the man and of You Are There.