At the end of the 21st century, the world has changed dramatically, but life continues 1,000 feet below the ocean's surface. In Great Britain, sea creatures swim among the ruins of Big Ben and the Tower of London, and citizens waver between fear and hope: fear of what lurks in the abyss and hope that humanity will soon discover a way to reclaim the planet. Meanwhile, 16-year-old Leyla McQueen has her own problems to deal with. Her father's been arrested, accused of taking advantage of victims of the Seasickness — a malaise that consumes people, often claiming their lives. But Leyla knows he's innocent, and all she's interested in is getting him back so that their lives can return to normal.
When she's picked to race in the London Submersible Marathon, Leyla gets the chance to secure his freedom: The Prime Minister promises the champion whatever their heart desires. The race takes an unexpected turn, though, and presents her with an opportunity she never wanted: Leyla must venture outside of London for the first time in her life, to find and rescue her father herself. Now, she'll have to brave the waters and defy a corrupt government determined to keep its secrets, all the while dealing with a secretive, hotheaded companion she never asked for. As she discovers a world drowning in lies, how much longer can Leyla hold out hope for the truth? If she fails or falls prey to her own fears, she risks capture — or worse. And her father might be lost forever.