Wealthy
big-game hunter Maston Thrust Jr. has a multimillion-dollar company, Thrust Inc., which drills for oil under the polar caps with a human-operated laser drill called the "Polar Borer". Following one expedition, only one man, geologist Chuck Wade, returns; he explains that the drill was going through a routine check in the icecaps when it surfaced into a valley super-heated by a volcano. When the crew, except for Wade, began exploring the area, they were killed by a
Tyrannosaurus rex. Maston decides to go there himself to study the creature. He brings with him Wade; Bunta, a Maasai tracker; Dr. Kawamoto; and Frankie Banks, a
Pulitzer Prize-winning photographer selected by the press pool. Matson is initially unwilling to let Frankie join the crew, but she manages to convince him to allow her on the expedition by seducing him. Upon arriving at the isolated valley using the Polar Borer, the group notices
Pteranodons. Once they raft to shore, they narrowly avoid being trampled by a
Uintatherium. After setting up camp, Maston, Wade, Bunta, and Frankie go out looking for the Tyrannosaurus, while Kawamoto remains at the camp. The party encounters the Tyrannosaurus and narrowly escapes from it. Later, the Tyrannosaurus finds the camp, destroying it and killing Kawamoto. It then takes the Polar Borer and throws it into a canyon full of bones. He uses the Borer to dig a canyon wall and releases a
Triceratops, and the two dinosaurs clash. After a fierce battle, the Tyrannosaurus kills the Triceratops. The group returns to the destroyed camp and notices Kawamoto and Polar Borer have disappeared. Enraged, Maston vows to kill the dinosaur. After a few months pass, the group is now living in a cave and has a number of encounters with
cavemen in the area, but are able to turn them away with a handmade crossbow. They also befriend a cavewoman, who they name Hazel. While Hazel helps Frankie wash her hair, the Tyrannosaurus returns. Frankie takes refuge in a cave, with the Tyrannosaurus trying to get in. Maston, Bunta, and Wade are able to turn it away with a large boulder tied to its tail. Maston decides to kill the Tyrannosaurus once and for all with a catapult. After building the catapult, they wait for the dinosaur. Out hunting, Wade finds the Polar Borer and realizes it is still operable. However, Maston refuses to leave, wanting to kill the Tyrannosaurus. Wade and Frankie leave the camp to get the Borer fixed and then leave, while Maston and Bunta remain. Once the Borer is launched back in the water, Frankie goes back to convince the others to leave with them one last time. Bunta is killed by the Tyrannosaurus while stalking him. Frankie reunites with Maston and helps him use the catapult on the Tyrannosaurus. But the dinosaur soon gets back to its feet and destroys the catapult. In the wake of the destruction, Wade arrives and states that they have to leave now or they will be trapped in the valley. Frankie pleads with Maston to go with them and to leave the Tyrannosaurus as it is the "last one", Maston replies "So am I". Wade and Frankie then leave aboard the Polar Borer, leaving Maston in the valley with Hazel. ==Cast==