Between 1941 and 1944, British intelligence dropped 16,000 homing pigeons in an arc across Nazi-occupied Europe as part of a spy operation code-named Columba. Returning to the secret government branch in charge of the "Special Pigeon Service," the birds carried messages that offered a glimpse of life under the German occupation. Written on tiny pieces of rice paper tucked into canisters and tied to the birds' legs, these messages were sometimes comic, often tragic, and occasionally invaluable, reporting details of German troop movements and new Nazi weapons. Here Gordon Corera tells the story of this subversive ploy, including the "Leopold Vindictive" network—a small group of Belgian villagers led by an extraordinarily brave priest named Joseph Raskin.