Des Kinvig leads a particularly dull life: when he isn't spending his time running his somewhat unsuccessful electrical repair shop, or moping about the pokey upstairs flat he shares with his fussing wife, Netta, and their dog Cuddly, he whiles away the hours daydreaming of better things. However, all that is about to change… On one particular day, having spent his time lazing about his shop, discussing U.F.O. sightings and governmental cover-ups with his unemployed - and unemployable - friend, Jim Piper, and generally avoiding doing any actual repair work – much to the irritation of his long-suffering customers – Des encounters a particularly attractive woman named Miss Griffin, who asks him to cut a spare set of keys for her. Needless to say, Des falls asleep before he can finish the job, and when Miss Griffin later returns, she flies into a rage and angrily vows to inflict bodily harm on the lethargic repairman unless he completes her order by the following morning. That night, Des wakes from a mysterious dream in which he hears Miss Griffin calling for help; unable to go back to sleep, Des takes Cuddly for a walk outside – and promptly comes across a giant alien spaceship parked on a piece of waste ground. Entering the vessel, Des meets three strange aliens named Loon, Bat and Sagga, and learns to his astonishment that their commander is none other than Miss Griffin, now wearing a revealing space-age costume and asking for his help in a much friendlier fashion. It seems that Miss Griffin is really from a race of people descended from the ancient Atlanteans, who left Earth thousands of years ago, and who now live inside the hollow interior of the planet Mercury; her mission is to watch over the Earth, but her spaceship has broken down, and only Des can fix it. Des eagerly complies, and his quick repair work earns Miss Griffin's respect, and a passionate kiss too boot. The extraterrestrial lovely then tells Des that he must keep her dual identity a secret, as she may well call on his assistance again in the future…