The Supreme Council from the Emerald Planet sends the superhero Starman (Super Giant in Japan) to protect Earth from destruction by an evil alien race from the Sapphire Galaxy. The Sapphirians are out to destroy earth using a space station that can hurl a fiery "Death Star" and destroy the entire planet. Starman tries to destroy their ship, but a meteor storm intervenes. Starman arrives on Earth and discovers Dr. Yanamaka, one of Earth's top scientists and his two children have been abducted by human agents of the Sapphirians. Worse, a huge conspiracy is afoot. A secret headquarters underneath a graveyard is the Earth headquarters of the Sapphirian takeover efforts. Starman arrives to rescue Yanamaka and his children, but they have been taken by rocket to the large space station that controls the Death Star. After knocking out the subsurface facility, Starman streaks into space in a second attempt to rescue the abductees. On the space station, Dr. Yanamaka's daughter, Kaoru, and Asami, a loyal team member, have done a lot to throw obstructions in the way of the Sapphirians. They are on the verge of escaping when the Sapphirians gain the upper hand. Yanamaka and the kids are about to be executed when Starman arrives. As Starman keeps the Sapphirian troops engaged, Dr. Yanamaka, his son and Asami escape in the Sapphirian rocket. Starman finishes off the battle and flies Kaoru to the ship. From there, they destroy the Sapphirian space-wheel base.
—Garon Smith