After the events of Across the Sea of Suns, small groups of humans have settled on other star systems. However, there is a constant threat from the Mechs, a civilization of machines left over from other civilizations and evolved to see all biological civilization as unstable and dangerous. Great Sky River tells the story of the Bishop family, who fight for their very existence on the planet Snowglade, which has been taken over by the Mechs. The Bishops are one of a number of families on Snowglade, all named for chess pieces. These "families" are more like clans or tribes. All use cybernetic implants and mechanical aids to enhance their perceptions and physical abilities. Personalities of dead members of the Family can be stored in memory tabs and accessed by plugging them into ports implanted in the neck. Bodily functions, such as the sexual drive, can be turned off to remove distractions. The Families seem to be equipped for long conflicts and periods of privation, continually migrating to avoid the Mechs.