The narrative follows Dr. Gryce's three companions—his bereaved children Martt and Francine and family friend Frank Elgon—as they answer a dying plea to find the missing Brett in a universe the scientist theorizes to be an atom within a vastly larger world. Their search propels them through bewildering changes of scale and into encounters with strange, often hostile phenomena, from a fog-borne menace to frantic rides across altered landscapes and violent struggles atop towering parapets. The story balances intimate grief and urgent rescue, tracing the trio's efforts to navigate unfamiliar magnitudes of existence and uncover what has become of their lost kin.