At the end of the 21st century the world has changed dramatically, and London is underwater. Sea creatures swim among the ruins of Big Ben, but 16-year-old Leyla has her own problems to deal with. Her father's been arrested, accused of taking advantage of victims of the Seasickness - a debilitating malaise that consumes people, often claiming their lives. When Leyla's picked to race in the action-packed London Submersible Marathon, she gets the chance to secure his freedom. But things do not go as planned, and if she fails she risks capture - and her father might be lost forever.