During construction of a subterranean factory of the ISO, Galactor attacks and a drill falls into a crack in the Earth. Since the energy source of the drill is uranium, it is predicted that, when the drill touches the magma, a huge earthquake with a magnitude of more than 8 will occur.
The Science Ninja Team, together with the geologist Dr. Karig, goes to collect the drill in an Earth investigation car, with the G-4 in the lead. The time limit is ten hours. On their way, they encounter an ambush from a mecha. Ken gets into the G-4 and, acting as bait, lures the mecha away from the car. He then shoots his boomerang, converted into a time bomb, into the mecha.
Soon the wagon is stopped by a rock layer. Joe and the others want to have the rock detonated by the monkey brought along by Dr. Karig, but from the monkey's collar, Katse's voice is heard. Karig's family is held as hostage and he accompanied them as a spy. G-4 returns to them and then digs its way just below the drill.
Through Katse's message, Dr. Karig learns that he has been abandoned. He wants to stop the detonation by having the monkey bite through a cable in the interior of the drill. But the mecha appears and starts attacking them. Ken has the timebomb explode. The descent of the drill is stopped by the explosion, but Dr. Karig is buried beneath the drill and loses his life.
Looking after the drill, which is collected by a crane, Jinpei takes away the receiver on the monkey's collar and stamps on it.