The only human child living in a human work colony on the Martian satellite Phobos, little Margaret Bain has devised a system for keeping the suffocating demons of boredom and loneliness at bay: she invents six imaginary companions, each an extension of her own personality, to play with. When the unproductive Phobos project is shut down, and after Margaret is forced to return to Earth with her parents, the child's other selves are lost to her. But they are not gone. Left behind, each one flourishes--refining its own persona, acquiring its own history--before ultimately dispersing to far-flung destinations throughout the universe.