A pragmatic and resourceful young woman originally from a Texas ranch, Millie works as an editor for the Federal Writers' Project in 1936. She sends most of her meager earnings home to her aunt and uncle, who are raising six boys through the hardships of the Dust Bowl. Driven by a strong sense of justice and a deep curiosity about people's lives, she views her work as a vital form of journalism. After physically defending a coworker from an assault, she is reassigned to investigate a struggling field office in Missoula, Montana.

A 19-year-old librarian in Missoula, Montana, Alice lives a privileged but highly sheltered life. Due to a history of childhood illness and the death of her mother, she is strictly protected by her wealthy father. Seeking purpose and eager to share the joy of reading, she conceives the idea of a Boxcar Library to serve remote lumber and mining camps. Her project is her first significant attempt to claim personal agency and define a life outside her father's control.

The daughter of a French-Canadian miner, Colette grows up in the harsh environment of Hell Raisin' Gulch. She inherits her father's passion for storytelling and his dedication to fighting for workers' rights against exploitative mining monopolies. Fiercely independent and deeply affected by the violence of corporate greed, she develops a hardened exterior to survive the dangers of the American West. She often travels disguised as a man, relying on her wits and a shotgun for protection.

The heir to a local mining fortune in Missoula, Sidney presents himself as a cynical, hedonistic rogue. This abrasive persona serves as a mask to hide the severe psychological trauma he carries from his service in World War I, where he lost his entire platoon. Despite his wealthy background and apparent apathy, he harbors a quiet empathy for those who suffer and utilizes his skills as a photographer to document reality.

A charismatic organizer for the Industrial Workers of the World, Finn arrives in Montana to rally miners against dangerous working conditions. He is a skilled orator who knows how to de-escalate violence and inspire loyalty among the workers. Handsome and driven, he forms a close bond with Colette and her father through their shared labor activism.

A French-Canadian miner living in Hell Raisin' Gulch, Claude is a dedicated union organizer and aspiring actor. He works secretly to rally his fellow miners against the oppressive Anaconda Copper Mining Company, enduring physical beatings for his efforts. He finds solace in literature, frequently reciting Shakespeare from memory to offer his peers a temporary escape from their grueling labor.

The right-hand man to Missoula's mayor, Mac serves as a driver, bodyguard, and paternal figure to Alice Monroe. He is fiercely loyal to his employer and takes his duty to protect Alice very seriously. While kind to her, his overprotective nature reinforces the sheltered environment Alice wishes to escape.

A successful author of pulp noir novels, Oscar works as a writer for the Federal Writers' Project in 1936. He approaches the project with a degree of cynicism but possesses a sharp, analytical mind. He becomes an observant partner in Millie's investigation into their office's poor performance.

A vivacious secretary with dreams of moving to Hollywood, Flo is a key member of the Missoula FWP team. She handles the office's clerical work and shipping logistics. With her social intelligence and wit, she quickly becomes an essential ally and confidante to Millie.

A reserved academic and cartographer, Thomas is one of the more cooperative members of the Missoula Federal Writers' Project staff. He focuses on meticulous research and cataloging local lore, showing a genuine dedication to the historical aspects of the guidebook.

A high-ranking executive for the Federal Writers' Project, Katherine is sharp, authoritative, and deeply committed to the American Guide Series. Rather than firing Millie for her insubordination, Katherine recognizes her potential and strategically reassigns her to fix the failing Montana field office.

The powerful mayor of Missoula and Alice's father. He is deeply entangled in Montana's complex political machinery. Having lost his wife and dealt with his daughter's childhood illnesses, he is intensely overprotective of Alice, preferring to keep her safe within the comforts of their privileged life.

Sidney's mother and a powerful social matron in Missoula. She represents the conservative elite, actively opposing the Boxcar Library out of fear that educating the working class will incite labor strikes and violence. She wields her wealth and influence to maintain the profitable social order.

An infamous bootlegger operating in Montana. Josephine is a tough, pragmatic survivor who understands the harsh realities of violence in the West. She provides a cautious, realistic perspective on the physical and moral costs of surviving outside the law.

The widow of Sidney's wartime friend, Sofia lives a backbreaking, impoverished life on her homestead. She fiercely demands that the writers document the unvarnished, painful truth of her reality rather than romanticizing the difficulties of rural life for their guidebook.

A local mine owner in Missoula. Though initially wary of the concept, he agrees to provide and outfit a repurposed train car for Alice's project, provided she can secure the necessary book donations from the community.

A young German miner working in Hell Raisin' Gulch. He rejects the union organizers, accusing them of moralizing from a position of relative privilege while his family struggles simply to survive the grueling mining conditions.