From the introduction: Beneath the surface of the ocean, the people of Icarus found a new frontier to explore. With the lands of earth massively overpopulated, these new pioneers settled on the miles of open aquatic land below and built the bones of a new city- one where nature and humanity could cohabitate better than the earth above. Over thousands of years, some of their bodies adapted to this environment, evolving lungs that could process water as well as they could air, and webbed fingers and toes. This small but vital evolutionary change was the catalyst for the massive growth of Icarus, a thriving city that now reaches its tentacles wide across the ocean floor.