(The world balance as it existed in 1963 is assumed to be still in place, although Britain now holds the neutral position once held by Switzerland.)

The theme of the novel is embodied in a conversation between two of the US spacecraft's crew as they begin exploring Achilles, which appears to have a benign and predominantly grassy environment.

One of them feels uneasy in this landscape and suggests a similarity of their position to fish in a pond on earth "swimming around thinking fishy thoughts".

The crew member comments "Well, what if we're like those bloody fish, swimming about our own little pond, and not knowing something else is very near us."

This fictional milestone was eclipsed by reality soon after publication, when Valentina Tereshkova became the first woman in space on Vostok 6 in June 1963.