After a close call with a hostile alien life form on the comet Twonkus-3, Jimmy returns home only to find that a cute and cuddly alien has stowed away on his ship. Despite Jimmy's warnings about the dangers of keeping alien pets, the twonkies become huge hits, and soon everyone owns one. But when the twonkies undergo an unexpected mutation, they threaten to take over Retroville! Invention: Remote-powered mini comet.