[1][2][3][4][5] In Autumn of the year 1988, contact with Space Station Terra is lost while sightings of UFOs are being reported all over America.

A follow-up investigation headed by UN scientist Professor Schmidt (William Ross) and his men is started to look into the strange reports.

UN team member Miyoshi (Kensaku Morita) visits world-renowned Professor Takigawa (Ryō Ikebe) and tells him that the UN is ordering him to complete construction of the space defense unit he created, Gohten, so that they use it to fight back the invaders, but he refuses saying that the project was disbanded three years ago when there were fears of an alien invasion of Earth.

While leaving, Miyoshi and Muroi along with Fuyuki (Hiroshi Miyauchi) see Professor Schmidt drive up to Takigawa's house, when he was reported dead.

After hearing of the incident, the UN puts Commander Oshi (Akihiko Hirata) in charge of the defense forces.

Meanwhile, the UFOs launch a full-scale attack on earth's cites, including New York City, London, Paris, Moscow, and San Francisco.

The Gohten makes it to Venus and Miyoshi, Muroi and Jimmy use a small lander to find the alien spaceship.

Miyoshi, Fuyuki and several crewmen go out in the lander to get on board the Daimakan, while Muroi, Jimmy and other pilots try to destroy the spaceship's force field with their space fighters while also fending off UFOs.

Miyoshi is successful in rescuing June, but not before battling and defeating the Space Beastman (most likely an animal from the alien homeworld).

Just when it seems the Gohten has the superior firepower, the Daimakan fires a large energy beam it had hidden under its frontal cannons.

He detached the drill from the Gohten with him inside and launched it into the Daimakan, causing it to crash into an active volcano.