In the last days of the twenty-first century, sea creatures swim through the ruins of London. Trapped in the abyss, humankind wavers between fear and hope—fear of what lurks in the depths around them, and hope that they might one day find a way back to the surface.
When sixteen-year-old submersible racer Leyla McQueen is chosen to participate in the prestigious annual marathon, she sees an opportunity to save her father, who has been arrested on false charges. The Prime Minister promises the champion whatever their heart desires. But the race takes an unexpected turn, forcing Leyla to make an impossible choice.