On the rainy afternoon of Wednesday, October 27, Kalin prepares to leave his apartment. His mother, Allison March, questions him, and he tells her he is going camping with friends for two nights. Before he goes, she reminds him that he is cursed, warning that he will lose what he loves most if he ever touches a gun. Kalin promises there are no guns and leaves.

He walks to the paddocks, finds Paddock A empty, and hears Navidad and Mouse in Paddock B. He leads them out, passing through the first two of the nine gates, then moves the horses up through the foothills. After collecting the supplies he and Tom cached in a miner’s shack, he struggles to saddle Navidad in the downpour, slipping in the mud and cutting his cheek on the saddle’s cantle. He pulls on a pair of black boots Tom gave him, as well as a white Stetson, and heads for Isatch Canyon. At the parking lot, he hears Tom Gatestone’s distinctive whistle and finds Tom’s ghost waiting on a pale horse. Tom has no memory of dying but understands their mission. They ride into the canyon together.

Earlier that summer, Landry Gatestone, Tom’s 15-year-old adopted sister, secretly tracked the boys’ rides all summer and later overheard Tom’s deathbed oath. That afternoon she discovered the horses in Paddock B; sneaking out after dinner, she finds both paddocks empty and hides as one of Old Porch’s younger sons, Russel Porch, pulls up, discovers the vacancy in a panic, and speeds off. Landry resolves to retrieve her horse, Jojo, and pursue Kalin.

Russel spots Kalin and the horses from two high vantage points and drives to Egan Porch’s house, where his father, Orwin “Old Porch” Porch hosts a poker game with sons Egan, Kelly, Woolsey, and Francis, along with slaughterhouse workers Trent Riddle and Billings Gale. During the game, Old Porch takes a call from a U.S. Senator confirming that a federal land bill central to his Four Summits ski resort project is advancing toward a vote.

Russel arrives, announces the horses are gone, and identifies Kalin as the thief headed for Isatch Canyon. Though the horses are worth nothing to him, Old Porch lets Russel pursue because he sees that Russel is eager to prove himself. Egan tells him to take his powerful horse, Cavalry. To embolden himself, Russel first goes to Egan’s gun cabinet and takes the Porch family heirloom, a Colt Peacemaker revolver, before concealing it and mounting up. Egan bets Old Porch $100 that Russel will fail.

Riding Cavalry into the dark canyon, Russel briefly experiences a liberating joy before spotting Kalin’s campfire and confronting him at gunpoint. Kalin ignores the weapon and offers food. Landry then drops from a boulder and knocks Russel off his horse, seizing the Colt.

The three share Kalin’s meal around the fire. Kalin explains he is fulfilling his oath to Tom. Landry tells the boys the canyon is haunted, recounting the story of the massacred Timpanogos and Katanogos, including Chief Pareyarts’s wife, who was cornered and named her killers, including the Porches and the Gatestones, before dying by suicide.

To placate Russel, Landry produces a $20 banknote, writes a bill of sale for both horses on its back, has Russel sign it, and lets him keep the document. They part on good terms; Landry keeps the Colt but promises to return it. Russel returns to Egan’s to find the mood has turned: Riddle has won a large pot, provoking Old Porch’s drunken fury. When Russel boasts that he nearly had to use a gun, Egan discovers the Colt is missing. Confronted, Russel admits Landry Gatestone has it. Old Porch strikes, then belts Russel. During the assault, Russel falls onto a shard of a crystal tumbler Old Porch had earlier thrown and shattered; the glass pierces Russel’s neck. Old Porch wrenches out the shard, fatally opening the wound. Russel bleeds to death.

Billings Gale takes control, cleaning the scene. Old Porch and Egan smear Russel’s blood on Cavalry to frame Kalin for the killing. Old Porch then calls the police and claims Kalin stole his horses and murdered his son.

After Russel departs, Kalin breaks camp and moves the group deeper into the canyon to avoid detection. Tom’s ghost warns that Landry does not belong on the journey, but she refuses to leave and helps repack the horses. Tom lights the path with a spectral firebrand drawn from his scabbard, casting a strange light that erases the landscape’s clear boundaries. They pass through a geological scar Tom called the Gate of the Mountain before making camp in a large dry alcove under a cliff.

After tending the horses, Landry falls asleep almost immediately. Kalin and Tom talk quietly; Tom says he feels displaced and can recall almost nothing, not even his own death. Their laughter wakes Landry, and after some back-and-forth Kalin tells her she can come along as long as she can handle herself and her horse. A great white owl settles on a nearby fallen elm. Its presence calms Landry into sound sleep, but Tom watches it without gladness, and Kalin is left wondering whether the dead are still capable of fear.

Kalin’s mother, Allison March, works the night shift at the Rome University Theaters, consumed by anxiety. A co-worker approaches and asks whether Kalin is all right, mentioning that her uncle witnessed how devastated he was at Tom Gatestone’s funeral two weeks ago. Allison is surprised: She knew nothing of this close friendship. She learns Tom was a widely loved young cowboy and FFA president who died of cancer, and that their friendship likely centered on horses.

The mention of horses frightens Allison. Her own thoughts reveal that the gun curse she issued to Kalin was a fiction she invented when he was 10 to protect him from the influence of his abusive father, Connor Mayhew. Later that night, the theater manager brings a police officer to speak with her. The officer tells Allison that Kalin is in Isatch Canyon and will be retrieved in the morning. When she assumes horse theft, the officer says Kalin killed a boy and that multiple witnesses claim he cut the victim’s throat. Allison laughs in disbelief and flatly insists the police are wrong.

Kalin wakes before dawn on Thursday, October 28, and recalls a troubling dream in which old scars became visible on his body. He cooks a small breakfast, giving most of his share to Landry, who again refuses to go home.

He tapes cardboard to the horses’ hooves for protection on rough terrain, while Landry reveals she carries two Easyboots for Jojo. She also recalls her older brother, Evan’s death in the truck race with Egan Porch. They break camp, passing the fallen elm and head up-canyon until a rockslide blocks the trail, forcing them to the canyon floor. They follow the swollen creek upstream and climb to where a long, steep field of loose polished stone, later named Aster Scree, bars further passage.

As Kalin redistributes his loads, Landry confronts him about the one-sided conversations he keeps having. He admits he can see Tom. When she challenges him, he relays a detail Tom provides about a snaffle bit Landry once stole from her Aunt Lissie that she cannot dismiss. She oscillates between calling him “crazy” and believing him.

The sloping scree takes Kalin two attempts to ride Navidad through. Landry attempts the same slope on Jojo, but is forced to concede and head down-canyon instead. Before Kalin’s final ascent on Mouse, Landry offers him the Colt. He refuses to touch it but instructs her on safe handling, ensuring the hammer rests over an empty chamber. Mouse almost slides backward near the top, but Kalin shifts his weight to restore balance and they break through to safety.

Looking back through binoculars, Kalin watches Landry ride safely down-canyon, then spots a heavy police presence at the canyon entrance, far more than two stolen horses would explain.