The plot exists on three levels.
First there is the frame story, where, in the south of England in the 1920s, a struggling theatrical troupe is performing a musical about romantic intrigues at a finishing school for young women in the south of France. As well as weathering ongoing backstage dramas, and audiences that are smaller in number than the cast, two extra stressors arrive: a famous Hollywood film producer turns up to see the show, and Polly, the mousy assistant stage manager, is forced to go on when the leading lady breaks a leg. As Polly struggles to keep her cool while acting opposite the male lead who she secretly loves, the rest of the company backstab each other as they try to impress the impresario.
Next there is the musical itself. Four of the girls at the school are very forward and acquire boy friends, but Polly is shy and has nobody to take her to the carnival masked ball that night. Tony, a messenger boy from a dress shop, brings her a costume and the two young people are struck with each other. They meet again in the afternoon and reach an understanding, she pretending to be only a secretary, so as not to seem above him socially. He comes to the ball and, when unmasked, is recognised as a peer’s son. So Tony and Polly are both rich and can marry openly.
Thirdly, there are extensive fantasy sequences in the film, during which the characters’ dreams and hopes are enacted in music and dance without words.