After the first wave, only darkness remains. After the second, only the lucky escape. And after the third, only the unlucky survive. After the fourth wave, only one rule applies: trust no one. Now, it's the dawn of the fifth wave, and on a lonely stretch of highway, Cassie runs from Them. The beings who only look human, who roam the countryside killing anyone they see.

Sixteen-year-old Cassie Sullivan is trying to survive a world devastated by the waves of an alien invasion, while trying to save her five-year-old brother Sam from a training camp that was created by the Others (the aliens).