A massive solar storm erases the world's technological infrastructure and kills billions. While the remaining humans are struggling to adapt and survive, they notice that some among them have...changed. Rachel Wheeler finds herself alone in the city where violent survivors, known as zapheads, roam the streets, killing and destroying. Her only hope is to reach the mountains where her grandfather, a legendary survivalist, established a compound in preparation for doomsday.

Other survivors are fleeing the city, but zapheads aren't the only danger. Rogue bands of military soldiers want to impose their own order in the crumbling ruins of civilization. When Rachel discovers a 10-year-old boy, she vows to care for him even at the risk of her own life. And the zapheads are evolving, developing communal skills even as they lay waste to the society they will eventually replace.