Eighty thousand years ago, a brutal Wagabou attack on a sleepy Ulam cave dwelling causes much death and injury. Naoh distinguishes himself in the attack, killing a couple of the gorilla-like Wagabou. Nevertheless, the attack, followed by wolf depredations, leads to the extinguishing of the Ulams' fire. Even the flame kept in a small bone and hide receptacle and guarded by a special fire-keeper, who flounders while slogging through a lake, is lost. The ragged survivors, in miserable conditions, send forth Naoh, Amoukar, and Gaw to find "atra"--fire. A rival faction of the clan seeks to claim the receptacle and the quest for themselves, but an elder chief-figure restores it to Naoh. Crossing a savannah landscape, the three are treed by a pair of sabre-tooth cats. Trapped for some time, the men eat all the leaves of the perilously small tree before the cats leave. Continuing on, they hunger for meat, and Amoukar and Gaw quarrel. They see smoke in a distant forest, but arrive too late to capture the fire. Pawing through the ashes of the campfire, they find bones to gnaw, but stop in disgust as they uncover a humanoid skull. Stalking the cannibalistic Kzamma by the light of their campfire, they see two captive women (one is Ika, who we are soon to meet) hanging captive from a tree. While Amoukar and Gaw run a diversion, Naoh tries to steal fire, but ends up in a fight. He seriously injures two Kzamma, but not before being bitten in the groin. In the end, Naoh absconds with two fire sticks and rejoins his mates. They are soon approached by Ika. The men try to drive her off, but she follows, and eventually wins over Naoh by applying a vegetable poultice to his injured gonads while Amoukar and Gaw are off gathering gourds. The Kzamma have pursued, however, and are poised to attack in superior numbers when miraculously a herd of Wooly Mammoth enter the scene. Naoh wins the day when he approaches the head Mammoth and, supplicant, offers a handful of grass. The animal accepts the offering, and the herd drives off the Kzamma. That evening around the fire, the sexual tension is think. Amoukar makes a try for Ika, but she appeals to Naoh, who warns off Amoukar and--a fast healer--promptly mounts her himself, despite her screams and struggles, though the brief interlude seems to conclude in mutual satisfaction. The following day, Ika attempts to divert the men toward another route, but they ignore her. Later, Naoh seems on the verge of a discovering the stone age breakthrough of flint-knapping when a stone dislodged by Gaw hits Amoukar in the head; Ika's laughter is foreign and somewhat alarming to the men, who, we realize have not yet learned the art and luxury of laughter. The following morning, Ika runs off, and, later that day and to the disgust of his fellows, Naoh leads them in pursuit. They let him go on alone and, nearing Ikas village of mud and reed huts, Naoh bogs down in quicksand and is taken prisoner by her people, the Ivaka. Ika's more advanced people feed Naoh and watch laughing as he has sex with four of the plumper village girls. The following day, Naoh is moved to tears as he watches a demonstration of the wooden drill the villagers use to make fire. Meanwhile, Amoukar and Gaw, having gone in search of Naoh, are found in the quicksand. That night, Amoukar and Gaw escape with an armload of atlatls (another new technology) and with Naoh, whom they must club unconscious in order to bring along. Ika follows. Later, with loving looks, Naoh and Ika decorate one another with mud. Up a tree, Amoukar drops a rock onto Gaw's head, and all have a good laugh. Still later, Naoh mounts Ika but she soon turns onto her back and teaches him another position, to his delight. As this continues, Amoukar makes overtures to Gaw, but Gaw makes clear his refusal. Soon after, the four encounter their old Ulam rivals who challenged them at the outset of their quest. While Naoh and Amoukar reconnoiter, Gaw and Ika hang back at a cave; suddenly, a massive brown bear comes out of the darkness of the cave and mauls Gaw. As the others carry Gaw toward home and safety, the rival clansmen attack, demanding the fire the travelers carry with them. With their new stone-tipped spears and atlatls, they make short work of the Ulam ingrates, and even Ika getting in on the atlatl action. Returning to the main Ulam group, the people are overjoyed to see the travelers returning with fire. During the celebration, which takes place in the shallows of a lake, the original fire-keeper again falls with the receptacle into the water, extinguishing the flame. Naoh makes an oratory to a skeptical Ulam audience before sitting down with the drill to make fire. He soon becomes frustrated and Ika takes over, starting the fire and winning over the Ulam people in the process. That evening, as Amoukar regales his audience with tales of their epic quest and the injured Gaw enjoys the ministrations of a clanwoman around the roaring campfire, Naoh and Ikah sit side by side in the moonlight admiring her swelling tummy.