I really like books on the historical aspect of cryptology, and Mr. Belfield's book certainly belongs to the genre. He provides some interesting tidbits that other texts seemed to gloss over or treat in significantly less detail. This is especially true of his chapters on the Kryptos sculpture at CIA Headquarters and the Voynich Manuscript. But this becomes somewhat of a burden in some ways ... perhaps it's a matter of taste, but of all the great cryptological mysteries, he spends a huge amount of print on the Shugborough Shephard's Monument. What's that? Never heard of it ? ... me neither, and I found the chapter about it pretty dry. To be fair to Mr. Belfield, I purchased the book before it was actually available in the US (from amazon.co.uk, after a mention in the American Cryptogram Association's newsletter), so perhaps his British readers are more familiar with this particular mystery. He seems to delve at least briefly into virtually every possible nuance of why something is this way or that at Shugborough, despite the fact that some theories clearly have more merit than others, and I thought it just went on too long.
That being said, I still enjoyed the book, as will most crypto enthusiasts. Like I stated, treatment of the Voynich Manuscript and the Beale Papers have very detailed sections. I would have like to see a better refutation of the claims of some to have solved the Beale Ciphers, which seem to have virtually no merit whatsoever, and Mr. Belfield seems to have the intellectual horsepower to do so, but he doesn't really dwell on it for any significant time.
A few other minor quibbles: Mr. Belfield seems to inject a great deal of his own opinion, especially social and political, into the text. Comments about the flaws of modern western democracies or small fluffy dogs being the favorite of 'airheads' both now and in the past may provide a humorous touch for some, but for me they detracted from the overall academic treatment of these unsolved mysteries. And the fact that I agree with Mr. Belfield's opinions on some matters doens't change my mind ... they simply don't go well with his otherwise rigorous treatment of the book's main points. Some small errors crop up as well ... for example, the Zodiac Killer did not terrorize "Southern California", but rather was a Bay Area phenomenon who MAY have had connections to some other murders in SoCal. Such errors are inevitable in books based on fact, and this does not really detract from what is otherwise an interesting and informative book.
I don't want to sound like I'm quibbling, so I'll sum it up ... Overall, I liked Mr. Belfield's book, and I recommend it to crypto enthusiasts.