We all know about D-Day and how it changed the outcome of World War II. The success on the beaches of Normandy shaped the eventual outcome of the most deadly war in history. Ben Macintyre points out in his remarkable book Double Cross: The True Story of the D-Day Spies that 10 million people were dying in the war each year in the early 40’s, so delaying the end of the war by even a few months meant life for millions of people. Success or failure on D-Day meant life or death for millions of people.

What we don’t know about D-Day — or at least did not know until recently — is the impact spies had on the success of the invasion. Students of military history know that Nazi Germany kept troops several potential invasion points, from Norway to Bordeaux. This decentralization allowed the Allies to avoid the full firepower of the Nazi war machine. Thus keeping the exact invasion target secret was the highest priority for the Allies. Even better, making the Nazis think it was going to be somewhere else would save the lives of thousands of Allied soldiers.

And now we know that’s pretty much exactly what happened. The British spy system was so good that they had every German spy in their country identified and, for the most part, working as double agents. Together they coordinated a campaign that had the Germans thinking the invasion would likely be anywhere but Normandy.

If you like spy novels, you’ll love this true story. If you love World War II history, it is a must read. And if you think James Bond is a fantasy, you’ll surprisingly find some similarities in the cast of characters that Macintyre uncovers in his research.

A very fun book indeed.