A missile capable of destroying Earth has been fired by Planet 46.

While dodging a runaway planet out of its orbit, the crew discovers it is on a crash course to the planet Membrono. Assuming the planet is deserted, Steve discovers after seeing a flying saucer that this planet needs help to avoid the fatal impact.

A duo of wacky aliens, the Lilispatians, captures the commander of XL-7 for hostage to trap the upcoming `Mayflower 3' immigrant spaceship, in order to turn the occupants into slaves for their planet.

Dr Rootes provokes an incident at Space City Power Plant so an alien space ship can deliver an invasive plant species. Steve, Venus and Matt must accompany Dr Rootes to Planet Hedra in order to get an antidote to this sudden vegetal invasion.

Fireball XL-9 is attacked by a mysterious ship so XL-5 replaces it on patrol. Steve heads to the nearest refuelling station, but the crew find it deserted except for Boris and Griselda Space Spy, who plan to steal XL-5.

On planet Rejusca, Steve and Zoonie must rescue Venus from sun worshippers who plan to sacrifice her to their solar deity.