Cat, the halfbreed telepath hero of and , joins a research team on Refuge, homeworld of his mother's people, the Hydrans. Immediately, he finds trouble when he helps a Hydran woman escape human pursuers. The decimated Hydran population of Refuge is confined to a bleak "homeland," by a huge corporate state, Tau Biotech. Tau also controls Refuge's one unique natural resource, "Dreamfall." The tangible residue of cast-off thoughts from beautiful, enigmatic "cloud whales," dreamfall forms vast reefs, sacred to the Hydrans, but mere exploitable data to Tau. Caught between Tau and desperate Hydrans who fight to reclaim their world, Cat must somehow forge the ruins of the past into a means to defeat Tau's brutality to save his people—and himself.