Andreia brings Will to her undersea home, part of a hidden civilization inhabited by smugglers, hackers, treasure hunters, and traders—all members of a different species, driven to the edge of extinction by human diseases and climate change. As feelings between the two grow, the investigation into her brother’s death leads to a sinister plot by a fanatical cabal. Together, Will and Andreia must find a way to save both humanity and the ocean without imperiling the existence of her species.