Twenty-six-year-old Mildred Harnack moved from her hometown of Milwaukee to Germany in 1929 with her new German husband. As a teacher and student, she bore firsthand witness to the astounding rise of the Nazi party. In 1933, she began holding secret meetings in her apartment with a ragtag band of political activists that grew into the largest underground resistance group in Berlin. Once the war began, she became a valuable spy for the Allies, the only American involved in leadership of the German resistance. In this at once intimate and sweeping biography, Harnack's great-great-niece reconstructs her remarkable story—all the way to its cruelly tragic ending—using letters, diary entries, and incredible personal accounts, resulting in a nonfiction narrative that reads like a rich, revelatory, and absolutely thrilling novel.