The underwater city of Atargatis is the only bastion of the last humans, a genderless population of nearly identical clones. They share their ocean world with a sea-faring species, the Scorps, who have prophesied human extinction. As the day of that prophecy nears, Atargatis fearfully blocks the Scorp pilgrimage to their goddess in the deep ocean. The Scorps' only advocate among the humans, Senator Edessa, is convinced that the Scorps' true intention is to save humanity from the prophecy. But when Edessa's last ally is assassinated in a coup by his nemesis, all political pretense falls away and Edessa is no longer safe in Atargatis.