Shatter City — Scott Westerfeld

When the world sees Frey, they think they see her twin sister Rafi. Frey was raised to be Rafi's double, and now she's taken on the role . . . without anyone else knowing.

Her goal? To destroy the forces that created her.

But with the world watching and a rebellion rising, Frey is forced into a detour. Suddenly she is stranded on her own in Paz, a city where many of the citizens attempt to regulate their emotions through an interface on their arms. Paz is an easy place to get lost . . . and also an easy place to lose yourself.

As the city comes under a catastrophic attack, Frey must leave the shadows and enter the chaos of warfare - because there is no other way for her to find her missing sister and have her revenge against her murderous father.