Amagi Mountain (also known as Saru-yama or Monkey Mountain due to its indigenous monkey population) is discovered to be the home of a 50 meter tall giant monkey, after the animal had ingested green leaf walnuts laced with Helipron G from a nearby research facility (Helipron G, a hormone nutrient developed during World War II for the purpose of strengthening soldiers in battle is found to trigger rapid growth in monkeys following excessive consumption).

When Jun and Yuriko sight a UFO, it is discovered to be a lost space capsule that has returned to Earth after a trip to Mars. The unmanned capsule is found to contain two small gold spheres. Before the objects can be scientifically identified, however, they are stolen by a thief who mistakes them for real gold.

A strange disturbance in Tokyo upturns the ground and shakes the buildings as if something huge is moving beneath the foundations of the city. In the canal of the Imperial Palace, a large tentacle-like vine called Juran appears, frightening passersby. Following this incident, Jun, Ippei and Yuriko witness an underground attack on humans, as the vines try to suck blood from their victims. Dr. Ichinotani suspects that a giant plant has taken root beneath Tokyo.

When Yuriko investigates increased volcanic activity in the Mt. Fuji area, she learns the story of a modern-day Tarzan named Takeru, who is rumored to live in the region's dense woods since becoming lost within them 15 years ago. Meanwhile underground volcanic energy creates boiling temperatures in a lake at the foot of the mountain and a huge boulder erupts from the waters. Because the rock obstructs a main travel route, it is blasted apart with dynamite and the pieces are transported back into the forest. At one night, the pieces collect around a strange luminescent rock, creating an enormous rock monster called Gorgos that lives and breathes like an animal.

Jun, Yuriko, lppei and Dr. Ichinotani visit a laboratory near Mount Isa to learn more about the experiments of a researcher named Kimura. Kimura has developed a special nutrient called Honey Zelion, which he has fed to colonies of bees. Following an incident of vandalism at the greenhouse where the bees are stored, a giant mole called Mongula appears, terrorizing the farmland community.

Returning home from a party one night, Jun and company become lost in the outskirts of Tokyo. When Ippei and Takehara accidently stumble into a marsh, the group seeks refuge in a nearby Western-style mansion to help keep the two men warm.

When several boys discover a mysterious, lightweight meteorite, their teacher delivers the strange rock to Dr. Ichinotani in Tokyo. Under analysis, the meteorite which the children call garadama, is identified as being comprised of Tilsonite and is found to be emanating powerful radiowaves.

Under the cover of night, a mysterious man steals the Tilsonite rock from Tokyo's Astrophysics Research Institute. When a group of meteors is detected approaching the Earth, Jun and the others fear that an invasion from outer space is once again imminent.

After being trampled beneath the maddening rush of a crowded Tokyo train station, Yuriko discovers crowds of people volunteering to participate in a new experiment called the 1/8 Project. When Yuriko enquires into the nature of the project, she is accidently reduced to 1/8 her normal size.

Following the sighting of a UFO and the destruction of two J.S.D.F jets sent to investigate, a series of strange disappearances plagues Tokyo. When Yuriko witnesses a woman vanish before her eyes, she begins her own investigation.

Following the destruction of a fishing vessel by a gigantic octopus, the lone survivor named Yuzo, the son of the ship's captain, is washed ashore nearby Compass Island. He is rescued and cared for by the beautiful native girl, Anita and the two begin to develop affections for one another.

Returning from a pilot's conference in Hong Kong, Jun and Ippei's flight aboard a supersonic passenger jet is suddenly interrupted by a strange pocket of turbulence.