Lizzie, a longtime servant of an upperclass Park Avenue family, quits because she has not been paid for months. At an employment agency, she encounters Joan Smith and her young son. Joan is looking for a maid. Lizzie takes a liking to Joan and her child Bobby and negotiates a salary that is higher than what Joan was hoping to pay, but much lower than what she was getting before. Joan's husband, struggling insurance salesman Jimmy, is initially appalled at Lizzie's salary, but Joan gets him to reconsider.
Lizzie repeatedly persuades Joan to upgrade her family's lifestyle so they can mingle with the elite and Jimmy can make valuable business contacts. Joan then talks her husband into paying for it all, despite his strong reservations. It works. Jimmy is able to sell large policies to his new acquaintances.
Meanwhile, Joan's inventor brother, Kent Fletcher, meets and falls in love with Diana Abercrombie, newly returned from a European finishing school. She, however, is infatuated with married womanizer Warren Sherrill, though she does like Kent.
When Lizzie finds Diana and Warren together late one night, she tries to separate them. When that fails, she insists on speaking to Diana alone. She then reveals that she is Diana's mother. She secretly married Diana's father the day before he left for World War I. When he was killed, Lizzie agreed to let his wealthy parents raise Diana as their own, as she, then their upstairs maid, could not provide what they could. At first, Diana is hostile to Lizzie, but as time goes on, she comes to love her mother, breaks up with Warren and warms to Kent. Meanwhile, Lizzie finds love again, with Owen, the former butler of her former employer.
