The world has been overrun by hitherto unknown beasts. Society has collapsed: the power is gone, cars are abandoned across the highways, and anyone left is hiding from the terrifying creatures -- and one another. Thirteen-year-old Abdi and his five-year-old sister Alva are on the run. Their last hope is to escape through the forest and to the sea. As they recall the strange events that led to the beasts' arrival, and how the two of them got to where they were, they must ask themselves who they can trust and what they will do to survive.