When the team lands on Obelisk Island, they find the natives besieged by earthquakes. The natives welcome their visitors, because they believe the outsiders can stop the earthquakes. Furthermore, various natives inform the explorers that their angry god Gappa, is the source of the quakes. An earthquake causes one of the giant stone statues to collapse, revealing a hidden entrance to an underground cavern. They cautiously search the underground grotto, and discover a monstrous reptile egg.
More tremors cause the egg to roll over and crack open, revealing an infant prehistoric reptile.
The other members of the team are elated at the discovery, and they immediately inform their publishing magnate employer, who orders them to bring the creature to Playmate headquarters. They take the creature back to Japan, and it triples in size in a matter of weeks. The greedy publisher places the beast in the care of the scientist, who attempts to get to the bottom of the mystery. Back on Obelisk Island, two parental Gappas emerge from the primordial sludge within the underground cavern. They see the remains of the egg, and are incensed that their offspring is missing.