Joseph Rotblat worked on the Manhattan Project, then walked away from it in 1944 once it became clear Germany would not build an atomic bomb, the only scientist to leave the program on moral grounds. This film traces his path from Poland to Liverpool to Los Alamos, using archival footage, photographs, and interviews with colleagues and family to reconstruct a life spent trying to undo what nuclear weapons made possible. It follows him into the Pugwash Conferences, the gatherings of scientists from both sides of the Cold War that he helped found and later chaired, working to keep communication open between American and Soviet physicists even as governments stopped talking. That effort eventually won Rotblat and Pugwash the Nobel Peace Prize in 1995. The film treats him less as a hero than as a stubborn man who kept insisting scientists bore responsibility for their inventions, decades before that view became common. Interviews with fellow physicists fill in the arguments he had, and lost, along the way.