The title alludes to humans being figuratively thrown onto the inhospitable Moon, a parallel to fish making their way onto land in the evolution of amphibians.

The Central Computer runs every aspect of every person's life: it is the government, court, information source, and friend to every citizen.

The first half of the story deals with behaviors in the future society such as indoctrinations of celebrity heads-in-jars, negotiating with brontosaurus herds to figure out whom they will sacrifice to make burger patties, and Earth-themed "Disneylands" which come complete with snakes, sand and sunburns.

The protagonist grew up on a brontosaur ranch run by a no-nonsense rancher with little time for philosophical speculation, and finds solace in the quasi-dedication of the Texas Disneyland's inhabitants to authenticity.

The Central Computer decides to launch a military raid to eliminate the people, causing its own malfunctions.