Like its ambitious companion novel, Replica, this far-reaching novel by the powerhouse author of Before I Fall and the Delirium trilogy digs deep into questions of how to be a human being in a world where humanity cannot be taken for granted. In the world outside of the Haven Institute, Lyra and Caelum are finding it hard to be human--and Lyra, infected at Haven with a terrible disease, finds her symptoms are growing worse. When Caelum leaves without warning, Lyra follows him, seeking a pioneering organization in Philadelphia that might have a cure. But what they uncover there is a shocking connection to their past, even as their future seems in danger of collapsing.