The narrator is summoned to the home of the Gryce family and becomes involved in an ambitious experiment that permits travel through extremes of size and time. A small expedition is propelled into successively larger cosmic realms, encountering strange intelligences, alien landscapes, and existential hazards that challenge their understanding of space, time, and causality. The adventure alternates action with speculative exposition, using fantastical episodes to articulate an imaginative theory of an infinitely large universe and the human perspective altered by such voyages.