Constance Harding, Deanna Durbin, is an unhappy orphan about to graduate from Miss Wiggins' school for girls. Her only real relatives are members of the James Clinton family, but they show little interest in the teenager. She is brought to New York by one of their loyal butlers, George, Charles Coleman, where she moves in with a circle of snobs. The upperclass crowd looks down on her, yet Connie finds warmth and loyalty among the household staff, who become her true guides through an unfamiliar world.
Barbara Clinton, Helen Parrish, Connie's cousin, orders her to stop Ted Drake, Robert Stack, from riding with him without her present. Connie does her best to follow the directive, but in the process she embarrasses herself, even as she secretly harbors a blossoming love for Ted. When the Drake family announces a ball, the servants rally to support Connie—raising funds to buy her a stylish dress so she can shine among the guests.
Yet Barbara spreads a lie that curtails Connie's invitation to the ball, giving the young woman a painful setback. Heartbroken but not defeated, Connie learns that a limousine will be at her disposal until midnight, arranged by the very people who understand her better than their employers. Meanwhile, the Clinton car is briefly detained by the police due to the chauffeur's missing proof of ownership, a snag that looms large as the clock nears midnight.
At the ball, Connie’s voice and presence captivate the room. Ted notices her in the crowd, and he makes his move, trying to win her over with charm and warmth. Their brief moment of happiness culminates in a kiss as the hands of the clock creep toward midnight. Realizing the hour is late, Connie rushes away, leaving behind a single slipper that Ted soon discovers and vows to return to its rightful owner.
Barbara, furious at Connie’s growing influence and the disruption she has caused, confronts the night’s magic by firing all the servants who helped Connie. The next day brings more tension: Connie vanishes, and Uncle James scolds Grace Clinton, Barbara Clinton, and Walter Clinton for their hostile and indifferent treatment of Connie. In a last turn of hope, Connie returns to Miss Wiggins' school with the aim of becoming a music teacher, while Ted follows, determined to reconnect with her. The tale closes on a note of reconciliation as the couple reunites, choosing a life together beyond the boundaries that once divided them.
