Joan Smith, the wife of an insurance salesman and mother of a small boy, hires Lizzie as her maid and housekeeper even though her wages are more than the Smiths can afford. Because Lizzie is used to working on Park Avenue, Joan finds it necessary to live up to Lizzie's expectations, and buys nice crystal and other household objects rather than admit they don't own them. Joan's husband Jimmy is upset by the extravagance, but Joan convinces him that a good front will help his business. With Lizzie's help, she talks him into moving into a larger, more fashionable apartment near Park Avenue. Their improved social standing does help Jimmy's insurance business and soon they are mixing with the best society. Joan's brother, Kent Fletcher, falls in love with young socialite Diana Abercrombie, but Diana is in love with married playboy Warren Sherrill. When the Smiths rent a Long Island estate for the summer, Diana is a regular guest there, and, to Kent's displeasure, so is Sherrill. Lizzie is upset by Diana's relationship with Sherrill and after she overhears him invite Diana to his beach cottage, Lizzie warns her to keep away from him. When Diana is outraged by the maid's interference in her personal affairs, Lizzie reveals that she is Diana's real mother. She had worked as the Abercrombie's maid and secretly married their son, but wanting a better life for her child, she left her to be reared by the Abercrombies after her husband was killed in World War I. At first Diana is upset, but gradually she comes to care for Lizzie. She wants to acknowledge her mother, but Lizzie stops her, pointing out that she doesn't want to undo her sacrifice. Diana accepts her edict, and makes her mother happy when she tells her that she has broken off her friendship with Sherrill. Lizzie then steers her in Kent's direction while she herself considers a proposal from Owen the butler.