In a barren land, a shimmering glass dome houses the survivors of the Switch, the period when oxygen levels plunged and the green world withered. A state lottery meant a lucky few won safety, while the rest suffocated in the thin air. And now Alina, Quinn, and Bea--an unlikely trio, each with their own agendas, their own longings and fears--walk straight into the heart of danger. With two days' worth of oxygen in their tanks, they leave the dome. What will happen on the third day?