As the crisp, clear morning dawned on the first day of June 1943, offering a hard blue sky and perfect weather for flying, the spy sat in the passenger terminal of Portela Airport outside Lisbon waiting to make a phone call. The call would be a death warrant.

His vantage point was a wooden bench shoved up against a rear wall, and his eyes surveyed the hectic scene playing out in front of him with a professional watcher’s focus. It was just after six A.M., but the terminal was already crowded, a tempest of voices sweeping through the high-ceilinged room. It was a clamor fueled by desperation. Jammed into the boxlike space were men, women, and families determined to get a ticket on the 7:30 A.M. British Overseas Airways Corporation (BOAC) plane to Whitchurch Airport, England—a seat on the lifeboat that would be their escape from a Europe that was a rapidly sinking ship.