The aliens came to take the Earth from humans, but also to save it for them, to take humans away and also to become them. These riddles and the future of the world have Cassie's mind in a twist, but she can't think of them now--she has been betrayed. So has all her friends and everyone on Earth--first by the Others, and now by themselves. As Cassie, and all humanity, struggles on in their last days, they will have to decide which is more important--saving themselves, or saving the essence of humanity.