Thirteen-year-old Mayo Cornelius Higgins, known as M.C., lives with his family on a rocky outcropping halfway up Sarah's Mountain in the Ohio hills. The mountain belongs to his family by deed, granted in 1854 to Great-grandmother Sarah, a formerly enslaved woman who escaped north to freedom carrying a baby. M.C. loves the mountain, but something terrible looms above: a massive spoil heap of uprooted trees and earth left by strip miners who cleared the summit two years earlier. The half-congealed mound clings to the slope above the house, and M.C. has nightmares of it burying his family alive.
Each morning, M.C. checks his rabbit traps and sits atop his prized forty-foot steel pole, which stands in the yard amid piles of car junk. He won the pole by swimming the Ohio River, and from its bicycle seat he watches over his younger siblings Macie Pearl, Harper, and Lennie Pool. He keeps a secret friendship with Ben Killburn, a boy who lives on Kill's Mound across a deep ravine. The Killburns are considered "witchy" by hill people: the men have six fingers on each hand and six toes on each foot, and both men and women are said to heal wounds by touch. M.C.'s father, Jones Higgins, has warned him to stay away, so the boys communicate through animal calls and meet hidden in the ravine.
M.C. has pinned his hopes on James K. Lewis, a man traveling the hills with a tape recorder, collecting and preserving voices. Ben has told Lewis about M.C.'s mother, Banina, whose singing voice is extraordinary. M.C. is certain Lewis will make Banina a recording star, forcing the family to travel with her and thus escape the mountain. That same morning, M.C. encounters a strange girl on a footpath carrying a round green pack; she flees when she spots Ben in the trees.
Lewis arrives that day, lost and exhausted. M.C. leads him past the spoil heap, and Lewis warns that the mound absorbs rainwater and slides on oily seepage; given the steep grade, it will eventually crash down on the house below. Lewis agrees to return at evening to hear Banina sing. When Jones comes home from the steelyard, where he works as a day laborer, M.C. announces the visit and declares the family will travel with Banina once she makes records. Jones assumes Banina will simply bus to Nashville alone and return in two days, and M.C.'s plan collapses. He tries to warn Jones about the spoil heap, but Jones dismisses the danger. In a quiet moment, Jones shares the family's history: Sarah's flight to freedom, a mysterious chant in an African language passed from eldest son to eldest son, and the old deed granting Sarah claim to the mountainside. Jones says Sarah "climbs eternal," a reminder that she holds the family to the land. M.C. senses a deep bond with his father but cannot reconcile Jones's devotion to the mountain with the need to flee.
That evening, M.C. spots a glint of light moving through the hills and races to intercept it. The girl from the path blinds him with a powerful flashlight; he leaps for the beam, but she flicks it off and he hits the ground hard. He grabs her arm, discovers she carries a large knife, and impulsively kisses her. She tries to hurl the flashlight at his head, and M.C. uses his paring knife to make a shallow cut on her back to stop her. She flees, warning she will kill him if he bothers her again. Walking home, Banina whispers a secret: The steel pole marks the graves of all the family dead buried under the junk in the yard, and Jones will never leave because he will not abandon the ancestors.
Lewis returns that night to record Banina, whose voice fills the parlor with songs both haunting and peaceful. Afterward, Lewis raises the subject of the spoil heap. Jones insists it will slide harmlessly into the yard, harden in winter, and he will drag it away in sections. Lewis warns that the grade is too steep; momentum will bring it crashing down. M.C. realizes Jones's plan is only a way to justify staying.
Before dawn, Banina takes M.C. swimming in the lake, where they discover the girl's tent on the shore. After the family leaves, M.C. waits for her to emerge. She reveals she has been traveling alone since age fourteen, working to buy her own car. M.C. dives through a hidden underwater tunnel beneath the rocks, and the girl insists on trying it. Underwater, she panics; M.C. discovers she cannot swim at all. He drags her through the tunnel and hurls her to the surface. Afterward, she refuses to give her name, saying names and places mean nothing when they cannot be verified.
M.C. brings the girl home, where Jones charms her over his special potato soup. She finally reveals her name: Lurhetta Outlaw. Jones tells her the name likely means her ancestors had no protection from the law, and Lurhetta is moved. When three Killburn men arrive to deliver ice, Jones reacts with open hostility. Lurhetta is disgusted and challenges M.C. to prove he does not share his father's prejudice. That afternoon, M.C. takes Lurhetta to Kill's Mound, where the Killburn compound stuns them: houses linked overhead by rope and vine, children tending gardens, and a philosophy that no one owns the earth. Lurhetta bonds with the Killburns instantly, holding Ben's six-fingered hand without flinching, while M.C. feels displaced among people his father taught him to fear.
At twilight, Lewis returns but is out of recording tape. He gives Banina the cassette of her voice as a parting gift. Walking Lewis down the mountain, M.C. learns the truth: Lewis is only a collector who preserves voices he cannot sell. Banina's voice would not survive the stage, where producers would change her. M.C.'s dream of escape is gone. Back home, he lies to the children, saying Lewis will return. Banina sings a ring-song on the porch, a call-and-response cycling through each child's name, and the music cleanses some of M.C.'s sorrow. He waits for Lurhetta to come for supper, but she never appears.
Past midnight, M.C. wakes to dense fog. At the lake, Lurhetta's tent is gone. Her knife is stuck point-down in the ground where the tent stood, left deliberately for him. Carrying the knife home, M.C. plunges it into the mountainside behind the house. Earth and rock loosen, and an idea takes shape: He will build a wall between the house and the spoil heap.
He pulls a car fender from the junk pile and begins digging, packing dirt and rock around the metal. The children join in. Jones returns, watches, then brings a broken shovel and branches. M.C. insists on doing the work his way, declares he will work for Mr. Killburn next summer and live on his own terms, and screams Ben's name across the mountain. For the first time, Ben arrives openly at the house. Jones controls a visible shudder but speaks to Ben civilly. Then Jones crawls under the porch and drags out Great-grandmother Sarah's gravestone, markings still readable, and lays it on the growing wall. "Just one," he says. "That's all I can give you today." M.C. understands: Jones is releasing part of the past, one stone at a time. Ben fits the stone in and they pack dirt over it. As clouds mass overhead, M.C. shovels, Ben packs, and the children feed the wall with materials. The wall is rising.