In a spaceship that can travel at the speed of light, Ulysse, a journalist, sets off from Earth for the nearest solar system. He finds there a planet which resembles his own, but on Soror humans behave like animals, and are hunted by a civilised race of primates. Captured and sent to a research facility, Ulysse must convince the apes of their mutual origins. But such revelations will have always been greeted by prejudice and fear...