One of the ‘inventors’ of the nuclear bomb, Sir Joseph Rotblat very soon turned away from weapons research to make a prolonged and principled stand against the dangers of nuclear proliferation. A physicist of great brilliance, he metamorphosed into a campaigner of admired moral conviction and leadership. This series of dialogues between two leading ethical thinkers brings together the courage and humanity of Rotblat with the spiritual wisdom and global visionary outlook of Daisaku Ikeda, the leader of the world’s largest and most influential lay Buddhist organisation. Together they reflect on fundamental issues of war and peace, the ethics of nuclear deterrence and the trajectory of Joseph Rotblat’s career, from the Manhattan Project to the Pugwash Conference and his Nobel Prize. Rotblat’s life-long mantra was that scientists have a moral responsibility to save lives, not destroy them. The integrity of both writers emerges powerfully and inspiringly from their wide-ranging discussions, which serve as a stark warning against the dangers of a resurgent atomic weapons race.