The novel is set a few hundred years in the future, entirely on the fictional planet Isis, the fourth planet in orbit around an F5 star called Ra, in the constellation Indus, about five parsecs from earth's own sun in our Milky Way galaxy. What this means is that the author had a good deal of scientific information which she used to make informed guesses about what it could be like for people to live on a distant planet, one with thinner air than earth and a brighter sun that emits more ultraviolet light than our sun.

Hughes suggests that Isis would become a colony planet only after the more "comfortable" planets near earth were already in use. Humans would find the deeper valleys of the planet Isis more comfortable than the mountains—the air would be thicker and so easier to breathe, and it would screen...