Bay and Nathan are high-school seniors in the mountain town of Hailey, Idaho, and they are falling in love. Bay is fascinated by local history and collects stories from older residents of the town. Nathan, at six-foot six inches, towers over his close friends, Taki and Nick. His stepfather is enraged that Nathan's interest lies in science rather than basketball. He is studying fairy shrimp, and classmates call him "Shrimp" to mock him. When Nathan's mother, Carol, disappears, Nathan and Bay grow closer as they search for her. A friend of Carols tells them that an apocalyptic event is coming, and to stockpile supplies, so Nathan builds a hiding place at the farm his mother owns and stocks it with food and other necessities. Then Nathan is nearly killed by an unseen man with a rifle. Carol's car, empty but bloodied, is found in the bottom of a canyon. While Nathan and Taki are in the mountains, the predicted event occurs. Bay, with many others, is taken away and put to work on a chicken factory farm. When Nathan and Taki come down from the high country, they find fire, corpses, and empty homes and streets. But Bay has left a clue for Nathan, and amid the chaos, he sets out to find her.