The events in Quest for the Future are unified by the ideas about immortality. The novel's society of time travelers has given the desirability of immortality much thought and has concluded that immortality is desirable only if people are psychologically well-adjusted and nonviolent. The main character Peter Caxton has a more fundamental view of immortality and pursues it simply because life seems better than death.

The action of the novel is based on two premises. First, that like space, time is finite. It has an identifiable end that limits what time travelers can do. The second is that time consists of "probabilities" that can be manipulated to create alternate time lines in which unhappy people may be changed to well-adjusted ones. Time includes a "fold" that runs from A.D. 9812 back to 1977. While in this fold, people grow youthful; they may enter a time line in order to age.