Humanity has been ejected from Earth by enigmatic aliens trying to save cetaceans. Homo sapiens finds itself exiled to strongholds throughout the solar system, foremost of which is Luna. There, human beings live in great comfort with almost all of their needs met and very little to worry about. As a result, they are losing their minds.

Through the unremarkable antagonist Hildy, Varley asks what happens to human beings who lack challenges and who lack any real direction. Comforts there are aplenty in Luna.

Technology makes sex changes routine and has all but defeated death itself. So now what? Humanity has slumped into a self-absorbed torpor that would be bad enough if the unimaginably complex supercomputer that controls every aspect of Lunar life weren't on the edge of a catastrophic breakdown. Hildy gains an increasing awareness of this problem as the narrative progresses; and he (later she) manages to struggle out of the cocoon of smothering comfort that threatens to make humanity incapable of responding to the imminent central computer breakdown.