Beneath a well in Mount Iwami lies a dormant monster called Neronga, which was defeated by the samurai Ichiemon Murai in the Edo Period. Recently reawakened by the construction of a new power plant in Mount Iwami, only its roars are heard, and a wake of destruction is left all over the power plant. The Science Patrol suspects that Neronga is invisible, but when the monster attacks again, they find that it becomes visible when it absorbs electricity! The Science Patrol and the Self-Defense Forces' Mobile Super-Ray Corps prepare to guard another power plant, which is Neronga's next target. Can they succeed before disaster strikes? Will Ultraman arrive to fight the invisible menace?