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 key D-Day spies were just five in number, and one of the oddest military units ever assembled: a Peruvian playgirl, a Polish fighter pilot, a Serbian seducer, a wildly imaginative Spaniard, and a hysterical Frenchwoman. Their enterprise was saved from catastrophe by a shadowy sixth spy.