for Impostors by Scott Westerfeld
Deception. Risk. Betrayal. Redemption. Master storyteller Scott Westerfeld is at the top of his game, and back to his most famous realm.Frey and Rafi are inseparable . . . two edges of the same knife. But only one of them is ever seen in public.Frey is Rafi's twin sister-and her body double. Their powerful father has many enemies, and the world has grown dangerous as the old order falls apart. So while Rafi was raised to be the perfect daughter, Frey has been taught to kill. Her only purpose is to protect her sister, to sacrifice herself for Rafi if she must. When her father sends Frey in Rafi's place as collateral in a precarious deal, she becomes the perfect impostor. But Col, the son of a rival leader, is getting close enough to spot the killer inside her . . . .
Publisher description retrieved from Google Books.