Everyone follows the Rule of One. But Ava Goodwin, daughter of the head of the Texas Family Planning Division, has a secret—one her mother died to keep and her father has helped to hide for her entire life.She has an identical twin sister, Mira.For eighteen years Ava and Mira have lived as one, trading places day after day, maintaining an interchangeable existence down to the most telling detail. But when their charade is exposed, their worst nightmare begins. Now they must leave behind the father they love and fight for their lives.Branded as traitors, hunted as fugitives, and pushed to discover just how far they’ll go in order to stay alive, Ava and Mira rush headlong into a terrifying unknown.

    These fragments are the Shells: fragile wastelands of desert and rock, protected from the cold of space by a water shield. In the struggle for survival, its people have depended on ancient technology, controlled by the omnipresent Network, to sustain the entire population. But the Network is breaking down, water is sparse, and a complete societal collapse is imminent. As the stakes become clear, the inhabitants of the Shells begin to turn on each other, and appear headed for all-out civil war. Now the paths of several strangers will converge at the opportune moment. From a woman who seeks to protect her family as it's ripped apart to a prison warden hiding from his past, this unlikely group has little in common--but together, they may hold the key to saving humanity from its worst enemy: itself.