Thirteen-year-old John serves as the first-person narrator, feeling the heavy burden of leadership in his father's absence. Equipped with practical knowledge instilled by his dad, he acts as the primary decision-maker for his small group during a widespread Nevada power outage. He attempts to mask his intense anxiety by taking decisive, sometimes stubborn actions, such as meticulously marking miles on his arm with a Sharpie to track their progress.

At eleven years old, Stewart is two years younger than his brother John. Typically energetic and possessing extensive outdoor knowledge, he becomes uncharacteristically pessimistic and lethargic following an armed robbery at their home. He requires specific medical supplies to manage a chronic health condition, making the loss of their home's generator immediately life-threatening. Frustrated by his brother's controlling nature, he frequently acts out to assert his own agency.

Cleverly is a smart, clear-thinking girl around John's age who leaves her grandparents' home in Las Vegas to seek refuge at the Lockwood property. She constantly evaluates situations logically and serves as the voice of reason when John's judgment is clouded by anger or fear. She balances her independence with a deep sense of community care, ensuring her group makes smart strategic choices.

Clayton is a desperate man who organizes a group to rob the Lockwood boys at gunpoint shortly after the blackout begins. He strips the home of its vital water tanks, generator, and food, adopting an aggressive survival mentality. Despite his violent actions, he later shows signs of internal conflict and guilt over stealing from children.

Will is Cleverly's eight- or nine-year-old brother who joins the Lockwoods on their long journey. Initially appearing as a potential liability due to his youth and exhaustion, he quickly demonstrates resilience when given responsibilities. He pushes through the physical toll of the desert walk without complaining, proving his value to the group by aerating water and carrying supplies.

Jess is a teenager living at Brighton Ranch who shares a medical condition with Stewart. She manages her health requirements with a calm maturity that deeply impresses the Lockwood boys. She represents the safety and medical resources the boys desperately seek on their trek across the desert.

Jim is John and Stewart's father, a firm advocate of off-the-grid living and emergency preparedness. He stocked his remote Nevada homestead with a six-month supply of food, water tanks, and a generator. Although absent for the primary events of the story, his teachings on independence, community support, and perseverance heavily influence how his sons approach the crisis.

Nate is Jess's older brother who assumes control of Brighton Ranch while their father is away in Las Vegas. The widespread blackout triggers intense paranoia in him, leading him to aggressively guard resources and view outsiders as direct threats. He acts out of pure self-preservation, willing to threaten a family friend rather than offer assistance.

Spike is a gruff, muscular man traveling with his pregnant partner during the blackout. He possesses one of the Lockwoods' stolen gas cans in his truck bed, indicating his involvement with Clayton Presley's group. He acts ruthlessly on the highway, using intimidation to take essential supplies from the vulnerable kids.

Steph is Spike's pregnant traveling companion. Her physical vulnerability serves as Spike's primary motivation for his aggressive scavenging and alignment with Clayton Presley's group.

Mr. Yardley is a neighbor of the Lockwoods in the small remote town of Lund. He attends community meetings to gather information about the blackout and accepts shared water from the well-prepared Lockwoods before deciding to evacuate his family to Ely.

Mrs. Yardley is the Lockwoods' neighbor. Because she is close to her due date when the blackout hits, her family decides to evacuate the remote town of Lund to stay with her sister in a larger town, emphasizing the difficulty of isolated living.