Max is a 14-year-old boy who is unusually large for his age. His physical size and dark family history scare people in his town. Despite his intimidating appearance, he is deeply compassionate and carries the grief of losing his best friend, Kevin. He lives in the basement of his grandparents' house and often doubts his own intelligence. When he witnesses an injustice, his strong moral compass forces him to act.

Rachel is an eleven-year-old, skinny, red-haired girl with a deep love for reading. Because she constantly has her head in a book, she has earned the nickname Worm from her classmates. She uses her books and a miner's helmet, a gift from her late father, as a psychological shield against her abusive home environment. Her belief in the magic of stories helps her survive difficult situations.

The Undertaker is Rachel's tall, skinny stepfather who dresses entirely in black and drives an old hearse. He styles himself as a street preacher but behaves abusively toward his family at home. He expertly uses intimidation and deception to maintain control over his wife and stepdaughter. He presents himself as a victim to authorities when challenged.

The Dippy Hippie, also known as Dip, is a retired schoolteacher traveling the country alone following the death of his wife. He drives a brightly painted bus called the Prairie Schooner and embodies the peaceful counterculture of the 1960s. He is perceptive, quickly recognizing that Max and Rachel are good kids in a tough situation. He offers them food and safe passage.

Hobo Joe is a scrawny, energetic transient who travels across the United States by hopping freight trains. He embraces his lifestyle with relentless optimism and shares his survival skills with his fellow travelers. He provides food, guidance, and cheerful company to the runaways when they need it most.

Grim and Gram are Max's maternal grandparents who have raised him since his mother's death and his father's imprisonment. They worry about his future but show pride in his progress, providing the only stable home environment Max has known. They remain fiercely loyal to him when trouble arises.

Rachel's mother is a timid woman who wears an old-fashioned black dress and walks stiffly. She bears the physical and emotional scars of her husband's domestic violence. She finds herself too intimidated to stand up to his abuse and protect her daughter.

Frank and Joanie are a couple of traveling con artists who manipulate others for their own gain. Frank uses a fake leg injury to play on people's sympathies, while Joanie attempts to pry personal information out of Max and Rachel. They view the runaways as an opportunity for profit.

Kevin Avery was Max's brilliant, disabled best friend who passed away before the events of the story. Through his vivid memory, Kevin continues to serve as Max's moral compass. He inspires Max to read, act honorably, and view the world as a grand adventure.

Sheriff Goodman is a short, stocky law enforcement officer in Chivalry, Montana. He attempts to manage the dangerous situation involving the unstable mines and the conflicting stories of the runaways and the Undertaker. He uses a megaphone to issue warnings to those hiding in the tunnels.