In 1942, as World War II was raging, the Gestapo sent out an urgent message: “She is the most dangerous of all Allied spies. We must find and destroy her.” That spy was Virginia Hall, a young American woman who—rejected from the Foreign Service because of her gender and prosthetic leg—talked her way behind enemy lines in occupied France and went on to become one of the greatest (and most unlikely) spies in U.S. history.

Today I talk with Sonia Purnell, author of the book "A Woman of No Importance." Virginia quickly established a network of spies to blow up bridges and track German troop movements; she recruited and trained guerrilla fighters, arming them with weapons she called in from the skies. As “the limping lady of Lyon” and later “the Madonna of the Mountains,” she became legend. Eluding the Nazis hot on her tail, her face covering WANTED posters throughout Europe, Virginia refused orders to evacuate. Finally—her cover blown and her associates imprisoned or executed—she escaped in a grueling hike over the Pyrenees into Spain. But, adamant that she had “more lives to save,” she dove back in as soon as she could, helping lay the groundwork for the Allied liberation of France.