In a world prone to violent flooding, Britain, ravaged 20 years earlier by a deadly virus, has been largely cut off.
Survivors are few and far between, most of them infertile.
Children are a rare commodity. For 22-year-old Roza Polanski, life with her family in their isolated tower block is relatively comfortable.
But when a stranger called Aashay Kent arrives, everything changes.
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?