Set in a distant prehistoric past, the novel follows a small band of Neanderthals, referred to as "the people," during a spring migration to their summer home near a great waterfall. Their world is governed by instinct, shared telepathic pictures, and reverence for Oa, the earth-goddess they believe brought forth all life. The narrative unfolds almost entirely through the consciousness of Lok, a cheerful adult male who perceives the world through smell, sensation, and fragmented mental images rather than abstract thought.
Lok carries the young girl Liku, who clutches the little Oa, a naturally worn root figurine shaped like a great-bellied woman. They reach a familiar marsh crossing and discover that the log bridge they always use has vanished, the first sign their world has changed. The group gathers: Fa, a perceptive woman carrying a newborn infant called the "new one"; Ha, the most capable problem-solver; Nil, Ha's mate and the infant's nursing mother; the old woman, the revered elder who carries smoldering fire embers in a ball of clay; and Mal, the aging leader, weakened by a deep cough. During the crossing, Mal falls into freezing water, and the group huddles around him to share warmth. They climb the cliff path beside the waterfall and reach their summer terrace, a sheltered rock overhang high above the river. The old woman rekindles the fire and declares it awake.
As Mal's strength fails, he assigns tasks: Ha and Nil will gather wood, while Lok, Fa, and Liku search for food. That night, Lok catches an unfamiliar scent in the mist, belonging to no creature he has encountered, but is too drowsy to investigate. The next day, Fa discovers a doe killed by a saber-toothed cat, and they butcher it, an act they consider acceptable because they did not kill the animal. Lok notices strange smoke rising from the island in the river but dismisses it. When Nil returns from wood-gathering alone, she reports that Ha vanished near the river. His scent stops on the cliff face next to a second, unidentifiable scent.
The old woman takes command. She sends Fa to carry a meat offering to the ice women, enormous ice formations shaped like female bodies on the mountain, to petition Oa for Mal's recovery, and sends Lok to find Ha. Tracking the stranger's trail, Lok discovers the unknown figure lay flat above the overhang to spy on the people. Ha's scent ends at a ledge over the river. From the bank, Lok sees a dark shape climbing a birch tree on the island. He flees in terror. They return to find Mal dying. The people bury him in a fetal position with food and water, and the old woman declares that Oa has taken him into her belly.
The old woman names Lok the new leader. Sent to investigate the island, he climbs a tree and calls out, but the new people retreat. Then Liku screams: She and the new one are being carried across the river. At a clearing by a dead tree, a man across the water holds a stick that suddenly shortens as an arrow strikes near Lok's face. Attempting to cross, Lok hangs from bushes and sees the old woman's body drifting below the surface. He scrambles back to find the overhang's fire dead. Fa emerges from hiding and tells him men took the children and the old woman went to meet them. Following a trail of blood and milk to the river, Fa concludes that Nil and the old woman were killed.
Reduced to two, Lok and Fa return to the dead overhang. Fa spots a drifting log and tows it to the terrace, where additional logs jam against outlying rocks to form a crossing. On the island, they witness a man in antlers dancing while others beat a rhythmic pulse. Lok calls for Liku and hears her answer, but the new people seize weapons and the pair flees.
From a hiding place in the dead tree's hollow top, they observe the new people in daylight: narrow-faced, stick-thin, and starving, with skin Lok mistakes for bone masks. The new people have built a thorn-bush enclosure around their clearing. Their ritual artist, a broad-fronted man called Tuami, paints a stag on the ground while another man sacrifices a finger. Hunters, including one Lok identifies by his chestnut-colored hair, are blessed and sent out. Women arrive in a second canoe, among them the "fat woman," who nurses the new one. Fa mouths "milk," recognizing this woman is keeping the baby alive. Liku, leashed to a tree, befriends Tanakil, a thin girl among the new people.
That night the new people drink fermented honey until the camp collapses into stupor. Fa plans to take the new one and leap the thorn enclosure while Lok searches for Liku. She crawls toward a shelter, but a man's nightmare triggers chaos, and Fa is spotted and chased. Both escape over the thorns. Lok tracks Fa's blood to a swamp, where her footprints vanish at the water's edge.
Alone, Lok collapses in grief. A cognitive shift occurs: He discovers simile as a conscious tool, characterizing the new people as like a famished wolf, like honey, like the river, and like Oa. He hears splashing and finds Fa alive, hiding in the marsh after being wounded. In the abandoned clearing, they find Tuami's painting of a Neanderthal pinned to a painted stag, with raw meat and fermented honey left as offerings. They eat and drink, becoming wildly intoxicated before passing out.
Waking, they see the new people hauling canoes toward the terrace. Fa plans to distract the men while Lok grabs the new one. Instead, Lok encounters Tanakil nearby and seizes her. The chestnut-haired hunter charges but trips and falls over the cliff to his death. Lok accidentally breaks the rope holding the second canoe, which slides downhill and shatters. In the overhang, he finds Tanakil tied to a painted Neanderthal figure on the rock. He frees her, and her mother reclaims her. A massive tree sweeping down the swollen river catches Fa among its branches and carries her over the waterfall to her death.
The narrative perspective abruptly shifts. Lok is described from outside as "the red creature," a small, bowed figure with jutting brow ridges. The creature returns to the clearing and digs in the earth. Its foot lifts the little Oa that Liku once carried; its hand holds a small white bone, implied to be Liku's, evidence the new people killed and ate her. Tears form in its eye-caverns. It staggers to the overhang, curls beside the dead fire, and lies still.
The final chapter shifts to the
Homo sapiens' perspective. Tuami steers the surviving dugout across an enormous lake. Marlan, the old man and leader, sits diminished. Tanakil lies vacant-eyed, speaking only the word "Liku." Her mother Twal accuses Tuami and Marlan of giving her child to the devils and receiving back a changeling. Tuami has been grinding an ivory dagger to kill Marlan, but the impulse fades. Vivani, the fat woman, nurses the Neanderthal infant, shuddering with a love that is also fear. Tuami looks at the ivory and sees that the figures of Vivani and the child fit its shapeless haft: They are an answer. Marlan declares the Neanderthals live in darkness under the trees. Tuami peers ahead to see where the line of darkness along the distant shore might end, but the water stretches too far, and he cannot tell whether the darkness has an ending.