I bought this in a bookshop in Ambleside when I was on holiday. I was hoping that it was going to be like The Code Book by Simon Singh, but unfortunately it was nothing like it. It contained seven chapters with seven examples of codes. One chapter covered the infamous Beale papers (on which one of the National Treasure films is based), another the mystery behind the references in the Enigma Variations and another the Kryptos sculpture at the CIA headquarters.
It was an easy read and fairly enjoyable, but very little technical depth.