Aurora (Exodus, #3)

Much of Earth is underwater - in the high mountains at the top of the world Lily survives with her mother and her people ...but she feels trapped. Elsewhere, beneath the exclusive sky-cities that tower above the waves, Fox has been waiting too. But when Fox and Lily meet on a virtual plane, they realize the time has come to act. The world must be made whole again, even if it means losing each other! The third and final installment in the brilliantly imagined, hugely romantic and poetically told trilogy set in a frighteningly realistic future.