Carr’s book is painstakingly researched, and his use of sources constitutes his greatest strength. As a part of his research, he managed to have the Cohens’ FBI file declassified, which he uses to a great degree as his story builds to a climax with their eventual capture. Carr notes in his Introduction that other authors have written about the Cohens/Krogers but never within the same book. Indeed, his recounting of his quest to follow the American Cohens to the British archives is intriguing.