D-Day, 6 June 1944 was a victory of arms. But it was also a triumph for a different kind of operation: one of deceit, aimed at convincing the Nazis that Calais and Norway, not Normandy, were the targets of the invasion force. The deception involved every branch of Allied wartime intelligence. But at its heart was the "Double Cross System", a team of double agents controlled by the secret Twenty Committee.
The first message sent to Tom Thorne's phone was just a picture - the blurred image of a man's face, but Thorne had seen enough dead bodies to know that the man was no longer alive. But who was he? Who sent the photograph? And why? While the technical experts attempt to trace the sender, Thorne searches the bulletins for a reported death that matches the photograph. Then another picture arrives.