This is a solid, if a little dry and sometimes a bit out of date, high-level overview of cryptography as it is used on the Internet. There are no equations or lines of code, so if you're looking to implement anything this is the wrong book. However if you're looking to learn about IPSEC, public-key crypto, secret keys, SSL, virtual private networks and things like that this is the right book.
The familiar cryptographic couple Alice and Bob are used in many examples to illustrate four general types of attacks made by "Henry the Forger", "Peeping Tom", "Play-it-again Sam" and "Bailey the Switcher". These are used throughout the book and this really simplifies understanding of how various types of cryptography can be attacked. Another one of the strengths of this book is lots of useful pointers to other books and Internet sites to provide supplementary information.
I'm not going to give this book 5 stars because to me that's a perfect book. However I highly doubt you'll be disappointed with this book as an overview to cryptography and how it is used on the Internet.