The Sirius platoon goes to Planet Rio Grande where a freight train without passengers crashed. But the Sirius SDF special train Big One is taken over in this trap schemed by space pirate Guy Sander. In order to prevent a misuse of Big One by the space pirate, the Galaxy Railways Control Office orders the destruction of the train. Manabu cannot leave his colleague David who is held prisoner inside the Big One, so he disobeys the order and flies into the Big One alone to rescue his colleague...