In 1924, Alice Monroe’s project to start a Boxcar Library is being thwarted by a “polite war” waged by Mrs. Julia Walker, who believes educating workers is a bad idea. Desperate, Alice decides to ask Julia’s son, Sidney Walker, for help. Knowing he avoids her, she hides in the back of his parked Packard automobile. When she reveals herself on the road to Lolo, a startled Sidney nearly crashes the car. His extreme reaction reveals a deep-seated trauma from his time in World War I, causing Alice to see his hedonistic persona as a protective mask.

Sidney takes her to a rowdy tavern in Lolo, a town known for gambling. After briefly speaking with her, he leaves her at the bar and joins a poker game. Later, he finds Alice about to dance with a rancher and quickly takes her back to his car. On the drive home, Sidney presses a large sum of money into her hand for the library—Alice cannot tell whether it is his poker winnings or his own savings. He promises to use his influence to ensure the project succeeds, explaining that he too once needed books.

In Hell Raisin’ Gulch in 1920, Colette Durand argues with union organizer Finn Benson. He encourages her to leave her small town, arguing that she can do more for the labor movement in a larger city, but she counters that he is naive about the many barriers women face. Annoyed, Finn accuses her of having a limited worldview and leaves.

Weeks later, Finn stumbles to her porch, having been brutally beaten by an undercover detective who followed him back to his hotel and told him to stay out of town; the town might have been Butte, though Finn is uncertain. Colette and her father, Papa, bring him inside. As he recovers from a broken arm and other injuries, Colette nurses him. To comfort him through the pain, she reads aloud from Howard Pyle’s 1883 The Merry Adventures of Robin Hood. The next morning, as she finishes the book, a recovering Finn gently holds her wrist, creating a moment of connection between them.

In 1936, Millie, Sidney Walker, Oscar Dalton, and Flo set out on a research trip for the guide, heading toward Glacier National Park. In the car, Millie asks Sidney indirectly about the itinerary and his work as photographer. Sidney reveals that the sections he was working on—interviews with members of the Flathead and Blackfeet tribes—were not included in the shipment to Helena because he had taken over that section and was still working on it. He shares a personal connection to the issue of Indigenous rights, having served with men from the Osage Nation in the war. Millie suspects he held the work back to save it from the sabotage that destroyed the rest of the submissions, suggesting that he had advance knowledge and thus may have been responsible. Later, when Sidney and Flo are out of the car, Oscar leans forward and tells Millie he shares her suspicion, believing Sidney couldn’t bear to see his own work ruined.

In 1924, thanks to Sidney Walker’s intervention, Julia Walker ends her campaign against the Boxcar Library and even holds a book drive. Before leaving on a bootlegging run, Alice’s driver, Mac, tells her he needs to discuss something important upon his return. Alice focuses on hiring a librarian, but the first two candidates are unsuitable. The third, Joseph Cantor from Idaho, is promising until he suggests giving a children’s book to an adult new to reading—something Millie knows the proud miners would take as an insult. Discouraged, Alice stays late at the library. A stranger enters, dressed for the trail and carrying a shotgun, to inquire about the position. When Alice—who believes the stranger is a man—asks the same test question, the stranger gives a perfect, well-reasoned answer. The applicant then removes her hat, revealing that she is a woman and introducing herself as Colette Durand.

In 1921, Colette Durand becomes the head librarian of Hell Raisin’ Gulch. One evening, her father seems troubled and reminisces on his unrealized dream of becoming an actor. He urges her to remember a quote from Shakespeare’s As You Like It: “And this our life […] I would not change it” (151). Moments later, he tells her to go inside as two men approach the house. Hiding in the kitchen with a cast-iron pan, Colette overhears them demanding that her father give them something he found. He tells them that even if they take the proof, he will still know—implying that they have reason to silence him permanently. He yells for Colette to run just before a gunshot sounds. Rushing outside, Colette finds him dying from a chest wound. With his last breath, he repeats the Shakespearean quote before dying in her arms.

The morning after Colette’s father’s murder, Finn Benson arrives to find her in a state of shock beside her father’s body. He carries her inside, cleans her up, and puts her to bed. The local sheriff, who is likely in the pocket of the Company, dismisses the murder as the work of drifters. At the funeral, Colette steps up to deliver the eulogy but is overcome and cannot speak; spontaneously, the miners in attendance begin singing a union song in Colette’s father’s memory. Later that night, both Colette and Finn are stopped short when they enter her bedroom to find a new Browning shotgun resting by the nightstand. A few nights later, she tells Finn she will get justice for her father. Finn promises to investigate but warns her against doing anything foolish. Colette agrees, but both know she is lying.

In 1924, Alice hires Colette as the boxcar librarian, deciding that Colette is more than capable of handling the dangers of the job. As they begin organizing the hundreds of donated books, Colette mentions that her father, a miner, loved reciting Shakespeare. This prompts Alice to share her own passion for storytelling, explaining her belief that stories foster empathy and can counter hatred by revealing a shared humanity across cultures. Later, they visit the nearly finished boxcar. Colette asks why Alice, who is so passionate about the project, isn’t taking the librarian position herself. Alice explains that her protective father would never allow it. Colette challenges her, arguing that Alice should find a way to join the journey because the miners need to see someone caring about them—it might give them just enough hope to keep fighting.

Two months after her father’s murder in 1921, Colette, having found no clues at home, leaves Gulch for Butte. A union contact, Bert Collins, tells her that several Anaconda Company men frequent the M&M Cigar Store. Colette alters the pitch of her voice to pass as a man and joins a poker game with two Company men, Gallagher and Smith. After winning a large pot, she leaves. Gallagher follows her into an alley, demanding to know who she is. Colette reveals her identity and accuses the Company of killing her father. Gallagher coldly denies any knowledge of the murder and dismisses her father as insignificant. He contemptuously tells her to keep the money as a “sympathy gift” from the Company. Furious, Colette leaves the winnings for the union and catches a train west, now certain she must find the man who pulled the trigger.

In 1936, Millie, Flo, Oscar, and Sidney arrive at Hiawatha Lodge, a dude ranch on Wild Horse Island in Flathead Lake. At the communal dinner, Millie interviews the owner, Lewis Penwell, who is also a state legislator. Penwell explains that Montana politics are shaped by the Anaconda Copper Mining Company’s immense power, noting that he himself must play by their rules: He refuses to take their money but cannot afford to run afoul of them. He compares the Company’s influence to an aspen grove, whose trees appear separate but are all connected to a single, deep root system that cannot be removed without destroying the landscape. He tells Millie that while times are changing, the Company’s grip on the state remains nearly absolute, noting that empires only seem inevitable until they fall.