Maddie is a smart twelve-year-old girl living in Millerville, a suburb of Denver, Colorado. Frustrated by the constant weekly shuffling between her divorced parents' homes and the responsibilities of caring for her younger siblings, she craves independence. When a secret plan to host an unsupervised slumber party goes wrong, she wakes to find her entire town mysteriously evacuated. She must rely on her intelligence, resourcefulness, and prior camping knowledge to survive in a suddenly empty world.

Maddie's mother is a kind, social, and busy woman who manages a bustling household. She is married to Paul and cares for their baby, her stepsons, and Maddie. She maintains high expectations for chores and routines but remains affectionate with her daughter, finding personal balance through her meditation group.

Maddie's father is a relaxed, responsible man who lives with his new wife, Jennifer. He has taught Maddie important outdoor survival, camping, and practical skills that become vital to her independence. His home serves as one of Maddie's primary bases, and his past advice often guides her decision-making.

George is a loyal and affectionate dog who originally belonged to the Nortons, Maddie's neighbors. Left behind during the sudden evacuation, he bonds deeply with Maddie. George provides essential companionship, early warnings of approaching danger, and physical warmth, becoming her most vital tether to the world of the living.

The looters are a group of aggressive men, led by a highly violent individual Maddie dubs "Angry Voice." They travel through the evacuated area stealing valuables lacking serial numbers from abandoned businesses. They represent the dangerous erosion of civilized rules in the empty town and force Maddie to drastically alter her survival strategies to remain hidden.

Paul is Maddie's stepfather, married to her mother. He is a friendly, kind, and responsible parent to his twin boys, his new baby, and Maddie. Despite his genuine efforts to engage with Maddie in conversation, she often responds with quiet resentment or brief answers out of a lingering frustration over her blended family dynamics.

Jennifer is Maddie's stepmother, married to her dad. She is a busy, social professional who plays the flute and shares musical hobbies with her husband. Though she is consistently friendly toward her stepdaughter, Maddie keeps her at an emotional distance.

Elliot and James are Maddie's fourth-grade twin stepbrothers, the sons of Paul. Both are highly intelligent and enrolled in accelerated school programs. James is deaf, and the twins share a deeply bonded, communicative relationship that Maddie often observes with a quiet sense of envy.

Trevor is the infant son of Maddie's mother and Paul. He is a curious, happy, and needy baby. While Maddie loves him and sometimes enjoys caring for him, she resents the adult responsibilities his presence places on her shoulders, motivating her desire for a chore-free weekend.

Ashanti and Emma are Maddie's middle school friends. They conspire with Maddie to host an unsupervised, chore-free sleepover at her grandparents' vacant apartment. Their sudden inability to attend the sleepover leaves Maddie alone in the apartment on the night of the town-wide evacuation.