It is 2109. People are due to walk on the planet Mars, supervised by BUSSTOP- British and United States Scheme for Travel to Other Planets. Joe Mortimer and Bruce Dougall are the joint heads of the organisation. They led the pioneering flights as far as Mars and can foresee few problems. They are more concerned with the years of bad feeling simmering between them. Little do they realise the chain of events which will be unleashed by the flight of Ariadne One to Mars; events which take in the past, the present and which will rewrite the future of Earth.