A group of explorers are pulled to the bottom of the sea after their ship is attacked. They then discover the lost city of Atlantis, which is inhabited by creatures from another planet.
Paul Lavond is framed for murder and robbery by his associates and sent to the Devil's Island. Years later, when Paul escapes with the help of a scientist, he vows vengeance on his associates.
When his cattle begin to mysteriously disappear, rancher Jimmy Ryan looks for answers. He is soon horrified to learn that a giant dinosaur hiding in Hollow Mountain is eating his livestock.