The novel is a future history, set from 1994 to 2194. It tells the story, with chapters at 50-year intervals, of the exploration of the
Solar System, with space stations in Earth orbit, then Moon bases, and landings on
Mars in 2094,
Venus in 2144, and the asteroids. This is told through the Troon family, several members of which play an important part in the exploration of space, since they all feel "the outward urge", the desire to travel further into space. They all "hear the thin gnat-voices cry, star to faint star across the sky", a quote from
The Jolly Company by
Rupert Brooke. In 1994, "Ticker" Troon is killed foiling a Soviet missile attack on a British space station, and is later awarded a posthumous
Victoria Cross. In 2044, a major
nuclear war between the
Soviet Union and the West wipes out most of the
Northern Hemisphere. Inhabitants of the Southern Hemisphere—virtually the only survivors of humanity—call it the "Great Northern War", the far earlier
war of the same name seeming very minor in comparison. Only after hundreds of years, with radioactivity going down, do expeditions from the south start carefully exploring and preparing to re-colonise the ravaged northern hemisphere.
Brazil is left as the main world power, which then claims that "Space is a province of Brazil". However, Australia eventually emerges as a serious rival. Consequently, English and
Portuguese become contenders for the position of the major worldwide (eventually, Solar System-wide) language. Eventually, space explorers break away from the tutelage of both earthbound powers and establish themselves as a major third power, called simply "Space"; the Troon Family plays a major role in this as in many other events. ==Major themes==