The novel tells the story of an astronaut, Hal Bregg, who returns to Earth after a 127-year mission to Fomalhaut.^[1] Due to time dilation, the mission has lasted only 10 years for him, but on Earth he faces culture shock, as he finds the society transformed into a utopia, free of wars or violence, or even accidents.

For Hal, however, this new world is too comfortable, too safe. Earth is no longer home, it is "another, alien planet". Humans themselves have changed, having undergone a procedure called betrization, designed to neutralize all aggressive impulses. Its side effect is an extreme aversion to risk.^[2] Hal mistrusts this approach, seeing it as wrong. In particular, for an astronaut, he cannot agree with the opinion that space travel and space exploration are nothing but a youthful and dangerous adventurism. For Hal, this means that "...they have killed the man in man". He and the other returning astronauts are viewed with mistrust, seen as "resuscitated Neanderthals". They are alienated, outcasts, and subject to social pressure to undertake the betrization. The other choice is to leave Earth again and hope that once they come back, in several centuries, Earth's society is more familiar again.

In time, Hal marries a local girl, Eri, and comes to see the world her way, even disapproving of his youth's love, space expeditions. When he learns that members of his former crew are planning a mission to Sagittarius, he seems not to care, content to leave the stars to others. Hal still remembers his past, recalls the moon Kereneia, a magnificent canyon "made of red and pink gold, almost completely transparent...through it you can see all the strata, geological folds, anticlines and synclines...all this is weightless, floating and seeming to smile at you". Yet he trades the chance to experience such sights and adventures for love and a peaceful, quiet life.