Gene has managed to make the most out of life at sea--salvage, smuggling, and the occasional crab shipment. Despite his incredible debt to the Black Lagoon mafia and the tricks his AI assistant plays on him, things are good. Until he finds a mermaid stuck in his exhaust pipe.
But this is not a world of magic and dragons. The Earth is almost completely covered with water. Most of the population has been driven out to corporate-owned Seaplexes--giant, spherical atolls that combine malls, mines, and shantytowns. But this appears to be a genuine half-woman, half-fish.
Gene brings the mermaid to a scientist friend on one of these stations. He studies her while Gene tries to secure his next job. As they decipher this affectionate girl's origins, complications arise when she is discovered by the seaplex's populace. More complications arise when Gene's land-born status earns him the ire of the station's riff-raff. Even more complications arise when rumors of sinking ships start to emerge.
Gene discovers more about the mermaid and has to reconcile his feelings for this non-human. He must return her to her home. But her home is something he never expected.