Red Queen by Victoria Aveyard
In seventeen-year-old Mare’s world, the Reds serve at the pleasure of the Silvers, only because of the color of their blood. Mare faces a life of servitude until she finds herself working in the Silver’s Royal Palace. Once her hidden powers are discovered, she is passed off as a long-lost Silver princess against her will and forced into an engagement to a Silver prince. As she begins to work for the covert Silver Guard resistance, she enters a world of secrets and the betrayal of her heart.