It's about the amazing second world war secret that was kept for thirty years after that the allies had been decoding the enemies secret messages on their coding machines.
A wonderful overview of how breaking the Enigma code affected the 'running' of the war.
Stunning in how often and in such detail the messages were read and stunning in how some generals ignored this invaluable source of intelligence!
If you liked this try Welchman's Hut six story!