In a world prone to violent flooding, Britain, ravaged 20 years earlier by a deadly virus, has been largely cut off from the rest of the world. Survivors are few and far between, most of them infertile. Children, the only hope for the future, are a rare commodity. For 22-year-old Roza Polanski, life with her family in their isolated tower block is relatively comfortable. She's safe, happy enough. But when a stranger called Aashay Kent arrives, everything changes. At first he's a welcome addition, his magnetism drawing the Polanskis out of their shells, promising an alternative to a lonely existence. But Roza can't shake the feeling that there's more to Aashay than he's letting on. Is there more to life beyond their isolated bubble? Is it true that children are being kidnapped? And what will it cost to find out?