A giant lizard-like monster emerges from an active volcano on a remote island, frightening the natives. They believe it to be an evil spirit of Monatabu, an evil witch doctor. When Samson and Goliath arrive at the village, the chief of the tribe tells them how they punished Monatabu by making him leap into the volcano. Ever since, his spirit returns every year to seek revenge. The boy and dog go into the volcano for investigation. Samson leaves Goliath, and finds the witch doctor is still alive. Not only that, but the monster is there, too, who is actually a prehistoric Iguanasaurus. Monatabu discovers Samson, and captures him by knocking him out with magic energy from his skull wand. Samson is then tied to a slab. Monatabu reveals that he befriended the Iguanasaurus when he entered the volcano. It is this beast that has been terrorizing the natives. Samson calls Goliath, who unties the ropes, and frees him. Then, Samson becomes the biblical strong man, and Goliath turns into a giant, Super Lion. When things get too tough, Samson uses Super Samson power to make himself and Goliath more powerful. Eventually, they seal Monatabu and the Iguanasaurus inside the volcano for keeps. When they leave, they tell the natives they no longer have anything to fear, and drive away on their motorcycle.