Estranged twenty-something half-siblings Cal and Erin return to their expansive Montana ranch, a place they once cherished, after their father falls into a coma and is placed on life support. With Erin's mother having passed away during childbirth and Cal's mother having died two years prior, their only familial support has been Valentina, the housekeeper and family friend, alongside Ace, a Kenyan nurse who provides vital care for their father. As the siblings come to terms with their father's grim condition, Cal, who harbors deep-seated resentment from past abuse, begins to sell and donate the ranch's possessions. Erin, still grappling with anger over their father's actions, plans to bring along Mr. T, the elderly family horse, back to her home in Hudson Valley, New York.
In a moment of vulnerability, Cal shares with Ace that their father's legal career was marred by a scandal involving the toxic secrecy of the Copperhead open-pit mine. Erin bravely reported the corruption, but this act of courage led to their father inflicting violence upon her and tragically claiming the life of her beloved horse, Pepper. This traumatic night forced Erin to escape, leading to a strained relationship where Cal eventually ceased searching for her.
Attempts at reconciliation see Cal opening up about his life in Cheyenne, Wyoming, and his aspirations of becoming a civil engineer, but Erin remains guarded. Undeterred, she purchases an old truck and horse trailer for transporting Mr. T, even as Cal expresses doubts about the truck's reliability. At this juncture, Mukki, the truck's seller, reveals his Mohican roots, linked to a family history steeped in fleeing violence.
Stranded by a truck breakdown, the siblings await the arrival of Joey, Valentina's son, with a tow truck. During this time, Erin reveals her culinary skills from her job at a restaurant that emphasizes whole-animal cooking. Together, they reflect at the Copperhead Mine, which Erin likens to Dante's seven circles of Hell, prompting a deeper contemplation of the American West’s mythos.
Chaos erupts when a thunderstorm leads to a power outage, jeopardizing their father's life-support system. As Ace endeavors to sustain their father's heartbeat, Erin finds herself thrust into action, manually pumping a bag valve mask to keep him alive. Upon restoration of power, Erin is confronted with a mix of relief and resentment for having saved the life of the man who caused her such pain. An emotional confrontation with Cal ensues, where she accuses him of cowardice for his failure to protect her from their father’s brutality — a confrontation that unearths Cal's guilt for his inaction.
That same night, under the guise of solitude, Cal expresses his frustrations about their father's unfulfilled life, only for Erin to witness the devastating moment he flatlines. While unconfirmed, it is heavily implied that Cal made the choice to disconnect his father from the life support. Ace covers for Cal, attributing the passing to complications from the earlier heart attack.
As the siblings prepare to chart their distinct paths, Erin requests that Cal keep in contact, to which he readily agrees. Ultimately, rather than taking Mr. T with her, Erin organizes for him to stay with Mukki at his ranch, ensuring the old horse has a caring home among friends.
