Does humanity depend on flesh and blood and being born of human parents? Is it possible for a machine to become human - to become too human? Philip Edge returns from a mission mapping the moons of Uranus to find that all of Earth's people have departed, leaving him to work out questions of humanity with only the help of a machine. Working from the belief that if a problem can be stated it can be solved, Edge finds that the answers are not what he ever would have expected.