Brad's swim coach at Washington High School has high hopes for his athlete. Exceptionally skilled in the water, Brad is expected to excel and win many competitions. But during a race, the high schooler collapses. He's diagnosed with an incurable disease that prevents him from ever swimming again, and his doctor doesn't expect him to survive more than five years. To save his life, he undergoes a difficult and unique operation that changes him into a mutant, which allows him to live underwater. He's alone at the beginning, but then he and his wife, Ada, start a new species called the Gill generation. Many others follow, creating the water world. It's first controlled by the individual countries that made them, and shortly after it becomes independent. This new society evolves beyond expectations, demanding rights from terrestrials through a revolution. The Gills succeed in controlling the entire planet utilizing advanced technology. With the continuous unrest and wars on land, many repatriate to water world. The existence and future of humanity rely on the new species, the Gill civilization.