On an Earth ravaged by global warming, human-dolphin hybrids called Aquarians have built thriving reef colonies among the drowned cities of the coast. Now their world is under siege from an enemy whose invisible weapon leaves no survivors. Only Ocypode the Atavism—half-human and half-Aquarian, marooned in the genetic limbo between species—knows why. Disclosing the reason could be as deadly to Aquarius as the Medusa plague itself. Ocypode and his comrades must face the perils of flight into the open ocean, a friend’s betrayal, a killer storm, a lethal kelp forest haunted by mutant monsters, and a fundamental challenge to their most cherished beliefs if they are to have any hope of saving Aquarius from destruction. They must enlist allies of the most unexpected sort from the most unlikely of places. Even then—when confronted by rogue scientists determined to resurrect the land by slaughtering the sea—it may not be enough.