Chloe Grace Moretz stars as Ohioan teenager Cassie Sullivan, whom we first meet in a post-apocalyptic world fighting for her survival. We flash back to how this world came to be, starting with the appearance of a massive alien spaceship in the sky. After four waves of cataclysmic "plagues" that include such things as tsunamis and a deadly virus, human beings begin to suspect that "the Others" are trying to take the planet and don't want humans on it when they do. Dealing with the separation from her family through a variety of mishaps, Cassie finds herself caught in the middle of a fight between the Others, who've been able to take over human bodies, and the last survivors of Earth, in a world where it's unclear who to trust.