In the early hours of June 6th, 1944, a Nazi secret agent, hidden away in a small suburban house in North London, wired a message to his handlers. The agent usually sent long rambling communications, but this one was more succinct than usual — and its implication was clear. The Allies had launched their invasion — D-Day had arrived. Before the largest armada in history had been spotted by the German defenders, this super-spy was warning of its approach. Astonishingly, however, the spy’s handlers weren’t listening. His message was not picked up for hours — by which time the Normandy landings were already underway. One of the most important warnings in history had been ignored. Not surprisingly, the spy was furious when he learned of his handlers’ failure. It felt like contempt. “I am very disgusted,” he transmitted. “I cannot accept excuses or negligence.” He warned them that they must listen in the future. They apologized profusely, so that when he sent another message two days later, …