"In wartime," Winston Churchill wrote, "truth is so precious that she should always be attended by a bodyguard of lies."

For Britain's counterintelligence operations, this meant finding the unlikeliest agent imaginable-a history professor named Alfred Vicary, handpicked by Churchill himself to expose a highly dangerous, but unknown, traitor.

The Nazis, however, have also chosen an unlikely agent: Catherine Blake, a beautiful widow of a war hero, a hospital volunteer - and a Nazi spy under direct orders from Hitler to uncover the Allied plans for D-Day...