In a stormy, desolate landscape, a group of modern-day hikers seek shelter in a shadowed cave and stumble into a framing tale told by an anthropologist. The expert, Conrad Nagel, interprets ancient carvings that introduce the saga of two rival tribes and a young caveman whose fate mirrors the strangers’ own struggle to survive in a world of danger and discovery.
Akhoba, Lon Chaney Jr., head of the Rock Tribe, leads a hunting party through a harsh wilderness. The group brings back a successful kill—a small Triceratops—that is cooked over an open fire. In the grim social order of the Rock Tribe, the strongest eat first, followed by the women and children, with the elderly scraping through the scraps. Tumak, Victor Mature, fights to defend his portion, insisting on his right to a share, and a brutal clash erupts when Akhoba knocks him over a cliff as his mother watches in horror. Tumak survives the fall only to be confronted by a new, more immediate danger—a mastodon that charges and drives him toward a river, where the beast sends him into the waters downstream.
Waking to the kindness of strangers, Tumak is found by Loana, Carole Landis of the Shell Tribe. Her people answer her shell horn call and carry him back to their cave, where a feast of vegetables is shared calmly, with meals arranged to feed the children, the women, and the elderly before the able-bodied men. Tumak’s arrival unsettles the Shells, whose orderly customs starkly contrast with the Rock Tribe’s brutal hierarchy. He learns to eat at their pace, guards his food with a wary eye, and watches as Loana invites him into a world where laughter and cooperation replace the violence he is used to.
Meanwhile, Akhoba, now injured after a muskox hunt gone wrong, watches as a younger hunter asserts himself and, against tradition, takes over leadership. The old ways crumble, and when Akhoba later staggers back to their cave, he is treated with cold disdain. Tumak’s quick adaptation to Shell life is rocky: he helps gather fruit by shaking trees for the children to collect, and the Shells show him how to laugh, something his old world had never taught him.
Tumak’s early attempts at hunting with the Shells yield both success and trouble. He uses a borrowed spear to kill an Allosaurus that traps a child in a tree, saving the youngster, yet his reluctance to return the spear to its owner foreshadows his ongoing friction with Shell leadership. The tension peaks when he steals the spear and a handmade hammer from their maker and confronts him when the maker tries to reclaim them. The Shell tribe’s leader banishes Tumak, pushing him away from Loana and the life he is only beginning to understand.
Loana, who has fallen in love with him, chooses to leave her people and follow Tumak. As they travel, they share a moment of simple companionship—Tumak plucks apples from a tree to feed them both, and Loana’s quiet care softens him. Their path leads them toward Shell Territory, where a giant armadillo-like creature and a clash of predators test their bond. A fissure trap during a clash between dinosaurs blocks their escape, but Loana manages to slip free, and Tumak arrives just in time to rescue her by defeating the leader who had displaced Akhoba and seized the throne.
With Tumak now seen as a capable leader, Loana takes charge of meals, a choice that confounds the Rock Tribe’s traditional order. She feeds the women and children first, then Akhoba, and only then the other elders; Tumak’s men are fed last. The following day, the Shell populace witness how the two tribes begin to blend their customs as Loana guides them toward a shared future. Yet a distant volcano roils in the landscape, exploding in ash and lava that scatters the Rock Tribe and cuts off Loana from her new friends.
Loana surfaces again with a rescued child on her back and reaches the Shell Tribe, only to find their cave endangered by a gigantic iguana-like dinosaur. Tumak, leading a small contingent, comes to her aid as Akhoba and the tribe hold the line with torches. An improvised plan unfolds: Tumak’s spear thrusts prove insufficient against the beast, but Akhoba counsels distraction and a strategic rockslide. The daring move succeeds, felling the threat and earning Akhoba newfound respect for his experience and wisdom. In a stirring moment of reconciliation, the two tribes unite as one people.
As the sun rises on a new era, Tumak, Loana, and the rescued child stand together at the threshold of a shared dawn. The ancient tale, once framed by carvings, becomes a living promise: a world where cooperation and courage can bridge old rivalries, and where love and leadership can guide a community toward a brighter future.
