In a far-future world where the former forms of life have become six small celestial bodies, immortal gems live on Earth under attack from the Lunarians. Phosphophyllite, whose body is especially fragile, is assigned to compile a natural history and, through repeated encounters and losses, comes closer to the origins of both self and world.

The gems, radiant yet fragile, live through vast spans of time while questioning the world they inhabit.

This short-story collection includes its title story, in which sentient spacecraft bound for another galaxy face trials that put humanity's survival at stake. Across five stories, scientific ideas meet urgent human choices amid an asteroid threat, observation during a pandemic, food shortages after a catastrophic eruption, and a confrontation between interstellar spacecraft.

Trials assail spacecraft that keep flying toward another galaxy for humanity's survival.