In the aftermath of a global solar flare that has decimated the human population and wreaked havoc on the world's power grid, Dr. Riley Poole embarks on a treacherous 1,500-mile journey to learn the fate of her two youngest children. After making the heart-wrenching choice to leave her injured teenage daughter, Julia, in the hands of her aunt and uncle, Riley and her new husband, Coop, strike out into the wilderness toward Colorado. Along the way, they cross paths with old acquaintances and combine resources to travel together. Riley and Coop soon get life-altering news and learn that one member of their group has put them in grave danger, forcing them to stay one step ahead of a hostile, newly formed government. Will Riley have the wit and courage to safely cross a continent and reunite with her family?