Mu Empire, which disappeared 12,000 years earlier strikes back. They use solar power and the live under the sea at the bottom of the Pacific ocean. Their wish to conquer the world again will be thwarted by a team of Japanese people. Former admiral Kosumi with his goddaughter, Makoto, photographer Susumu and his assistant Yoshito will manage to find Captain Jinguji, Makoto's father who is the constructor of the bigger and greatest submarine that ever manufactured named Atragon (aka Gotengo). This is the only man who can save the world but he hides at a secret location as he is still stubborn about Japan's loss at the World War II and his plans were about to place Japan at the top of the world. Hopefully the team will change his mind and an epic battle between the Muans and the human kind is about to start. This film is quite entertaining but it is not Toho's best production as the 'Mysterians' or 'Battle in outer space'. You can still enjoy it though.