The Fireball XL5 narrowly misses a planet that bas broken out of it's orbit and realize the planet is on a collision course for the planet Membrono. After concluding the planets are uninhabited, Steve realizes he saw a flying saucer and after the ship lands at Venus' house, the XL5 is lured back to save the planet Membrono from destruction.

Venus and Prof. Matic are about to set off in the Mayflower 3 to colonise the nearby planet, New Earth. But the Advance Scout has been kidnapped by two evil midgets who plan to hold the new immigrants captive.

The crew of XL5 encounter Boris and Griselda the space pirates on the Companion 12 space station.

The crew of the XL5 becomes entranced by a strange alien sphere and Robert is the only one who can save the crew.