James Wormold's wife has left him and he is now scraping a living in Havana as a vacuum cleaner salesman while looking after Milly, their teenage daughter to whom he is completely devoted. He is approached by a British intelligence officer named Hawthorne who offers him money to spy for his country. Struggling for money, Wormold accepts the offer - the trouble is he doesn't know the first thing about spying nor does he have any useful contacts or information. Loathe to give up his new source of income he hits upon the idea of inventing intelligence and fellow agents he has recruited. However, some of the names he chooses are those of real people living in Havana. Assuming that MI6 will lose interest unless he spices up his reports, Wormold sends sketches of vacuum cleaner parts, claiming they are from a secret communist nuclear base in the mountains. It's all going swimmingly until MI6 send him an assistant and wireless operator, Beatrice. Now he has to keep his misinformation from her as well as his paymasters! But when a news story reports that one of Wormold's fictitious sources has been killed in a suspicious car accident, the story takes a weird and dark turn. It seems the KGB has discovered that he's an M16 spy and they too believe his reports. Way out of his depth, Wormold is now on a desperate mission to save his other ‘sources’ whilst not being killed himself.
