The robot named Rex had been bought as a companion for Paul when the Simpsons decided to pioneer on Ganymede, a moon of Jupiter ...a rough, dangerous satellite where a small boy needed a strong, intelligent robot to protect him. By the time Paul is sixteen, they are inseparable. Robots, of course, have a personality leeway that gives each one a certain individuality within its pattered capacities - and Rex had a wonderful personality, with a logic quotient that allowed him to reason. But when the Simpson family is ordered back to Earth and Paul refuses to part with Rex, the robot plans to stow away on a spaceship to Earth - no easy feat, even for a robot with Rex's abilities. Thrilling chases in skimmers, through spaceports, and over the deserts of Mars are just the start of the problems for The Runaway Robot!