Professor Chardin has just killed a man. Before calling the police to turn himself in, he burns some leaves and a notebook in the fireplace. Secret agents in the street with listening devices flee when the police arrive. The professor refuses to be defended by a lawyer and to explain himself, but his friend Professor Carter and his wife come to his support and he agrees to explain his crime of inventing the H-bomb, the secret of which was stolen from him by his collaborator Rossi at the very moment when he had given up his research, convinced by Albert Einstein's pacifist plea and other personal circumstances.

Trois savants, sans cesse confrontés à la question de la vie après la mort, s'interrogent sur les progrès de la science, et prennent chacun des voies opposées.