The story begins in the near future on a tired Earth that has nearly been depleted of its resources. Food is scarce, and rationing is in effect. The government occasionally reduces the ration so that all of the teeming billions can receive an equal share. Bill Lerner, a young man of high-school age, lives in a huge apartment complex with his widowed father, George.

Bill and his father seize the opportunity to escape Earth when it is offered: the government is allowing a select few to emigrate to new worlds in the solar system, one of which is Ganymede, a moon of the planet Jupiter. Ganymede is not like Earth. Its environment is barren, dangerous, and hostile to humans, and the new inhabitants must "terraform" Ganymede, that is, use technology and engineering skills to reshape the planet to support terrestrial plants and animals. A certain amount of "social...