In World War II, there were mounting fears that Hitler was building an atomic bomb. Such a prospect depended on two of the world's top nuclear scientists; brilliant German physicist Werner Heisenberg, and his Danish mentor, Niels Bohr. In 1941, Heisenberg travelled 200 miles in secret to Copenhagen to meet Bohr. The meeting put both men at immense risk, and had a cataclysmic effect on their relationship. This film was made with access to their personal correspondence and newly released documents kept secret for half a century.