It's a scary thought: how different would the world be if the Nazis had developed a nuclear weapon first? We'll never know.
But we do have the ability to learn more about the covert operation by the Allies designed to disrupt the German nuke-building project. Science writer Sam Kean visits The Exchange for a fourth time to tell the story, as told in his book .We hear the story of a motley crew of operators who played a key part in winning World War II.