Navy Commander Harold Roberts (Jock Mahoney) and his crew, accompanied by reporter Maggie Hathaway (Shirley Patterson, calling herself Shawn Smith), are flying across Antarctica. They encounter a storm and almost collide with what looks like a Pterosaur. They are forced down by a bent control rod and, to their surprise, land below sea-level in a warm volcanic crater. They find a steaming tropical jungle with living dinosaurs, carnivorous plants, and human footprints. The radio will not work and the bent rod breaks when they try to repair it.

They encounter a man named Carl Hunter (Henry Brandon), the only survivor of a plane crash in 1947. He has built a fortress-like house, has a conch shell whose sound frightens off animals, and survives mostly by raiding the dinosaurs’ nests. He offers the remains of his plane to help them fix their copter, providing they leave Maggie with him. The crew resists, but they know their ship will leave in 25 days to avoid the Antarctic winter. They cannot find where he has hidden the plane and they debate leaving Maggie behind or torturing Hunter for the information. Commander Roberts will not stoop to either. Maggie is attacked by an Elasmosaurus and Hunter rescues her. Finally, Hunter gives them a map to find his plane.

They repair the copter and take off just as the T-Rex comes upon them. They fly to pick up Maggie and save Hunter from the Elasmosaurus and fly the man out of the place. Was that an option all along? The helicopter crashes in the sea and all are rescued. Harold and Maggie declare their love.

The film was directed by Virgil W. Vogel and produced by William Alland. It was going to be shot in color but they spent too much on dinosaurs, not that the T-Rex was that realistic.  Jack Arnold was supposed to direct a big-budget picture, but the budget was slashed and he quit. The music was actually by Henry Mancini. Most of the creatures were men in suits, puppets, and the usual monitor lizards. Tim Smyth was in the T-Rex suit. The head of the creature ended up under the stairs in the Munsters series (1964). The story was inspired by the discovery of warm water in Antarctica. When the evil truck in Steven Spielberg’s Duel went over the cliff, its growl was that of the T-Rex in this film. The poor creature eaten by the carnivorous plant instead of Maggie was said to be a tarsier, but it was actually a loris. Sorry, Loris. The monitor lizards were fast and scary, but even at twelve, I knew the T-Rex wasn’t very good, though I didn’t much care.