In 1943, Edda Mussolini, daughter of the fascist dictator, gave her father and Hitler an extraordinary ultimatum – release her husband, Italy’s former foreign minister, Galeazzo Ciano, from prison, or risk her leaking her husband’s incendiary diaries to the press. Instead, Hitler and Mussolini vowed to do everything in their power to destroy the diaries – even if it meant killing Edda. They ordered Hilde Beetz, a German spy...