A former soldier is caught working the black market and sent to prison while his partner escapes and goes on to become a gangster, but their paths cross again as they both fall in love with the same woman.

Astronomer Shinichi Tachibana has a secret identity as the superhero "Iron Sharp" and is well beloved by children. When they are attacked by a group of metallic aliens, Iron Sharp drives the aliens away. The resourceful Tachibana helps develop an electric barrier to block the aliens from coming to the Earth. After several losses by the aliens, they announce that they will invade the Earth, throwing the world into a state of panic.

Attracted by the report of the development of a new type of rocket fuel, the vicious dictator of Krangkor, the dark planet, descends on Earth to steal the formula from its creator, the benevolent Dr. Makin.