Ringer

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.
Though Gemma just wants to go back to her normal life after Haven, she soon learns that her powerful father has other plans for the replicas-unless she and her boyfriend Pete can stop him. But they soon learn that they aren't safe either. The Haven Institute wasn't destroyed after all, and now Gemma is the one behind the walls.
Bestselling author Lauren Oliver brings the Replica duology to a shocking close in Ringer, but like both Gemma and Lyra, you won't be able to leave the world of Haven behind after you've turned the last page.