Five vacationers and two crewmen become stranded on a tropical island near the equator. The island has little edible food for them to use as they try to live in a fungus covered hulk while repairing Kessei's yacht. Eventually they struggle over the food rations which were left behind by the former crew. Soon they discover something unfriendly there...
Mining engineer Shigeru investigates the disappearance and death of his fellow coworkers when prehistoric nymphs are discovered emerging from the mines. After an attack on the local village, Shigeru heads deeper into the mines only to make a more horrifying discovery in the form a prehistoric flying creature. Soon a second monster appears as the two converge in Fukuoka.
When a rare species of butterfly is found in a mysterious valley in Japan, a pair of entomologists go to investigate and find more. They discover Varan, a giant monster, who decides to leave the valley and head straight for Tokyo.
