Snow: The Double Life of a World War II Spy
Nigel West, Madoc Roberts
It's an interesting set of facts, and the level of research is commendable, but the writing isn't up to the task. Snow reads like a bureaucrat's report, even though the underlying material would make a tolerable thriller. A first-rate author, or even a good magazine editor, could have improved this immensely.
For a fast-paced and very readable introduction to the facts, I highly recommend Ben Macintyre's Double Cross. It's a long way from being deep, and I suspect that Macintyre was not nearly skeptical enough of his sources, but it's a fun read nonetheless.