Ringer

With its gripping companion novel, Replica, this remarkable novel by the author of Before I Fall and the Delirium trilogy asks how to be a human being, in a world where humanity cannot be taken for granted. In the world outside of the Haven Institute, the replicas 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.
But in trying to find a cure, they uncover a shocking connection to their past, even as their future seems in danger of collapsing. Gemma just wants to go back to her normal life after Haven. But soon, she learns that her powerful father has other plans for the replicas-unless she and her boyfriend Pete can stop him. Bestselling author Lauren Oliver brings the Replica duology to a shocking close in Ringer.
Like Gemma and Lyra, you won't be able to leave the world of Haven behind after you've turned the last page.