A caveman, Spear, returns from spear-fishing to find his wife, son and daughter devoured by a trio of red horned tyrannosaurids. Distraught, he contemplates suicide before resolving to take revenge. While fishing, he sees the silhouette of a dinosaur and, thinking it to be one of the red horned tyrannosaurids that killed his family, silently pursues it into a thicket. He comes face to face with the grayish-blue hornless Tyrannosaurus, Fang, with two offspring hiding behind her. The sight of the young dinosaurs causes Spear to back down, just as they are attacked by the red horned tyrannosaurid pack. Though Spear helps Fang kill the trio, their gargantuan alpha arrives and consumes Fang's babies while Fang watches helplessly. Spear and Fang slay the alpha, but Fang is left distraught over the loss of her children. Spear leaves Fang and walks off alone, but is later approached by Fang, and the two decide to travel together.