During the Stone Age, a small band of the Dark Tribe’s hunters return to their rocky desert home with their kill and are greeted with grunts of approval by the entire tribe. As the men prepare the meat for a feast, the surrounding mountains suddenly erupt, spilling molten lava and rocks onto the primitive village. As the tribe flees for their lives, the earth splits open, swallowing and killing most of them. Dragging themselves from beneath the devastation, the remaining tribe members then cheer as a battle ensues between Mak and Zen, the two men contending to replace their Old Leader, who is now dead. After Mak kills and beheads Zen, he demands to be blessed and given the leader’s sacred bone necklace by the Old Crone, the tribe’s elderly witch. After the tribe scavenges for any remaining bugs, mice and rabbits for nourishment, Mak leads them across great desert dunes to find a new home. When they come upon a fair-haired tribe, the Dark Tribe prepares for battle, but when they see that each tribe’s children easily play together, Mak and the Leader of the Fair Tribe decide on a truce and allow their people to mingle. That evening in a cave, the Dark Tribe watches as the Fair Tribespeople draw on the cave walls and drum and dance around the open fires. Soon after, the Fair Leader presents young Noo as a wife for Mak, who offers the leader a girl in exchange. After the Old Crone performs a ritualized whipping of the women surrounded by frenzied dancers, Mak and the fair leader have sex with their respective women. The girl’s mate tries to escape with her to save her from the Fair Leader’s bed, but they are soon crucified as punishment for disobeying. Later, the Dark Tribe moves on, taking Noo with them, and settles in a fertile valley where they flourish, domesticating goats, harvesting grains and living in small shelters. On the day that Noo dies giving birth to Mak’s twin sons, another member of the tribe gives birth to a mute baby girl. The tribe demands that she be sacrificed; however, after lightning suddenly strikes, the Old Crone decides the omen means that she should adopt the child as her apprentice. Years later, the twins, now adolescents, fight for their father’s attention. Dark-haired, sadistic Rool impresses his father with his fierce hunting skills, but the fair-haired Toomak, although gentle, outsmarts his brother with traps to catch game and wins his father’s favor. One day, as the brothers approach manhood, Rool attempts to rape the Dumb Girl, who manages to escape his grasp, but is then abducted by the Marauder Chief and his tribe. Toomak, having witnessed the scene from afar and having tender feelings for the Dumb Girl, leads Mak and the tribesmen to the Marauders’ cave, where a vicious battle ensues. After the Marauder Leader is mauled by a beast, then killed by Rool, the Dumb Girl fights the Marauder Leader’s vengeful daughter Nala until Toomak separates them. That night during the celebration of their victory, Toomak takes Nala for his lover, enraging a jealous Rool. Later, Mak, who has been wounded in battle, names Toomak as his successor and dies, but when Rool disputes the decision, a ritualized battle between the twins begins. Tribesmen wearing the head and skins of slaughtered beasts tie the two men at either end of a long rope. During the fight, Toomak and Rool lasso and lash each other, then fight with knives. When Toomak has Rool at his mercy, he stabs his leg instead of killing him and then throws down his weapon in disgust with the tribe’s violence. After burning his tent, Toomak leaves the village, taking Nala and half the tribe with him. Rool, consumed with hatred for his brother, decides to track him down despite his injury. With the remaining tribesmen, Rool walks into a dense forest, where men covered in river silt and wearing oversized grotesque masks attack them. Toomak and his men come to their rescue just in time and tear the masks off the Mud Men, revealing albinos who, fearing the sun, flee. Still consumed with destroying his brother, Rool abducts Nala and slips away with his three remaining men. The Dumb Girl, who has witnessed the battle, alerts Toomak to Rool’s escape, then follows closely as Toomak chases Rool and his few remaining men up a steep and wet, slippery stone cliff. Nala pushes one man to his death, but Rool continues up the incline with her and then stakes her to a pyre on the mountaintop. After disposing of Rool’s other men, Toomak reaches the top and battles his brother with a torch, while Rool tries to spear him. Meanwhile, Nala frees herself, but is then forced to wrestle a python trying to crush her. As Toomak saves Nala, the Dumb Girl crushes an effigy of Rool, then stabs him, sending the dark twin falling to his death. Toomak, Nala and the Dumb Girl stand together on the edge of the cliff, looking at the sky, where an apparition motions for them to come forward, into the future.