 Ineffectual dreamer Des Kinvig (Tony Haygarth) runs a rundown little electrical repair shop in the small town of Bingleton where he lives with his mumsy, scatterbrained wife Netta (Patsy Rowlands) and oversized pet dog Cuddly.One day his shop is visited by the beautiful, sharp-tongued Miss Griffin (Prunella Gee) who seems at first just another dissatisfied customer.However, after encountering a flying saucer while walking the dog one night, Kinvig discovers she is actually a scantily-clad alien from the planet Mercury who desperately needs the help of the scruffy, bearded Des' "exceptional brain" to stop an invasion of the evil ant-like Xux who are replacing people with robot duplicates.