On the evening that he is to dine at an exclusive club with his social-climbing fiancée, Roberta Trent, Michael Ashburn, the general manager of the Trafalgar Loan Company in London, finds himself in charge of watching "walking collateral," a pretty young woman named Julie Evans whose "uncle" has borrowed £400 against a pair of non-removable diamond earrings. Afraid of losing the earrings, Michael spends the evening with Julie, missing his dinner and winding up in jail for the night. The next morning, Roberta arrives at Michael's apartment, only to discover Julie in Michael's pajamas and her fiancé, who has just been released from jail, without a proper explanation. In the midst of Roberta's jealous wrath, Julie escapes and returns to her "uncle," Paul Douglas, a theatrical agent who has been hired by Roberta's father and Michael's boss, the newly rich Rufus Trent, to break up Michael's engagement. Julie's triumph over Roberta is short-lived, however, and although she has fallen in love with Michael, she agrees to continue the ruse in order to assure herself a starring role in Douglas' next show. In spite of Roberta's attempts at disposing of Julie and marrying Michael quickly, Julie's tricks and charms mesmerize the aristocrat. The scheme and Julie are exposed when thieves hired by Roberta steal the "unremovable" earrings in front of Michael. Eventually, however, Roberta's shallowness and Julie's sincerity are confirmed, and Michael proposes to Julie during her nightclub performance of "It Must Be Love."