The leading character is Fred, a home-built computer. Fred is not so much programmed as perverse, given to uttering loud and embarrassing remarks at inopportune moments. He all but ruins the courtship of his owner's daughter, Mary, by predicting she will marry a man with red hair and spectacles, a specification her fiance, Peter, doesn't happen to fit. Fred does, however, have his uses. He is able to forecast the weather with complete accuracy. News of this reaches the Met. Office, who send a spy down in the person of Albert Shorter, the assistant in charge of Mist and Drizzle, who poses as a believer in the occult and infiltrates the Shaw household. But Albert isn't the only one interested in Fred - Uncle Ben is trying to find out if Fred can predict the winner of 3.30.