The notorious Professor Challenger claims that dinosaurs still walk the earth.

When the press and the scientific community ridicule him, Challenger vows to show them proof. And so he sets off for South America, accompanied by a big game hunter, a scientist and a young reporter eager to impress the woman he loves.

On a remote plateau in the middle of impenetrable jungle, they discover the impossible truth, but must battle monsters and men before they can bring their testimony home.