In a world far from our own, Lissa has exposed a dangerous secret. Captive twins, known as Spares, have been the subjects of dark government experiments. And Lissa's own twin was one of their first victims. Running for their lives, Lissa and Lin discover another rebel faction of twins, and they believe they've found allies at last. But a terrifying threat they could never have expected is waiting in the shadows...Can Lissa protect Lin in a world that wants to destroy her?