Stanley Moon, a short order cook in a London hamburger bar, is desperately in love with Margaret, the waitress, but is too timid to approach her. Depressed by his dreary life and his inability to express his love, he decides to hang himself. Failing at even this, he is suddenly confronted by the mysterious George Spiggot, who is in fact the Devil. The forlorn Stanley agrees to sell his soul for seven wishes in the hope of winning Margaret's love. Spiggot consents to allow Stanley an escape clause should he find the fulfillment of his wishes unsatisfactory. He wishes first to become an articulate intellectual; but he makes the mistake of talking himself into almost raping poor Margaret. Next, he becomes a wealthy tycoon who lavishes everything upon Margaret, now his wife, only to discover that what she really wants is other men. His third wish makes Stanley a pop-singing idol; but he loses Margaret's love when she swoons over a more exciting newcomer who looks remarkably like Spiggot. Spiggot next tricks Stanley into squandering one of his wishes when Stanley wishes out loud to know what Margaret is doing at that moment. They become flies on a wall and are able to observe Margaret talking with Inspector Clarke, who is investigating Stanley's disappearance. Becoming desperate, Stanley decides to be a man of irresistible sex appeal. Despite Margaret's passion, however, she cannot bring herself to be unfaithful to her saint-like husband, who resembles Spiggot. As his next request Stanley pleads to be "a warm, loving, outgoing person and Margaret the same." The wish is granted, and they are transformed into nuns of the Order of the Leaping Berelians, whose mother superior again resembles Spiggot. After explaining to Stanley that one of his wishes was wasted on an ice lolly, Spiggot announces that he has reached his quota and that his soul will be restored to him in the hope that he, Spiggot, may reenter heaven. As Stanley returns to his hamburger bar, Spiggot is refused heavenly pardon because of his excessive pride.