When lawyer David Trent pays a visit to Emmet Mortimer's London home, Shirley, his overworked and unappreciated "wallflower" daughter, falls instantly in love with him. Determined to break out of her stifling home life, Shirley disguises herself as a dowdy, spectacled matron named Mrs. Halifax and wins a position as Trent's son's governess. As the Cockney Mrs. Halifax, Shirley dotes on Trent and scolds him when he drinks American-style cocktails or stays up too late to work on his legal briefs. After Trent secures an acquittal for Norman Harrington, a popular London painter who was accused of murdering his wife, he invites Harrington to his flat for a victory drink. While chatting with Trent, Harrington notices some of Shirley's hair slipping out of her wig and draws a youthful, flattering sketch of her. From the sketch, Trent finally recognizes Shirley but remains silent about his discovery and, knowing that she will be dining with her father the next night, finagles an invitation to join them. Although entranced by Shirley during the dinner, Trent feigns ignorance of her game until she tries to sneak back into his flat as Mrs. Halifax. After exposing her ruse, Trent confesses his love but, out of propriety, sends her to her friend's house for the night. The next morning, however, Shirley, unable to stay away, returns to Trent's flat as Mrs. Halifax. The romantic relationship blossoms until Trent's long-estranged wife shows up unexpectedly. Shocked by the appearance of Mrs. Trent, Shirley leaves Trent and becomes a model for Harrington, who soon falls in love with her. When Harrington asks Shirley to become his mistress, however, she rejects him and returns to her former dreary life at home. To the surprise of her family, a remorseful Harrington drops by to see Shirley one afternoon and proposes marriage. Seconds later, Trent arrives and, after explaining to Shirley that he had not seen his wife for four years, announces that he is securing a divorce. Thus assured of Trent's honor, Shirley eagerly accepts his love.