In this adaptation of Victor Herbert's operetta, a couple starring in a musical for six years are tempted by Hollywood but are deceived into separating.
Gwen Marlowe (Jeanette MacDonald) and Ernest Lane (Nelson Eddy) have played Sweethearts since their marriage six years ago. Producer Felix Lehman (Frank Morgan) fears that Norman Trumpett (Reginald Gardiner) will put them in the movies. Author Leo Kronk (Mischa Auer) arrives, and composer Oscar Engel (Herman Bing) conducts as Hans (Ray Bolger) dances, and Gwen sings "Wooden Shoes." Ernest sings to her "Every Lover Must Meet His Fate." Gwen and Ernest decline invitations so they can date. Ernest and Gwen sing "Sweethearts." Gwen gets a romantic note from Ernest every night. Leo and Oscar quarrel. Felix gets Gwen and Ernest to come to his party that is broadcast on radio. Felix, Leo, and Oscar speak. Ernest and Gwen sing "Pretty As a Picture." Hollywood producer Benjamin Silver calls Trumpett to get Marlowe and Lane. Trumpett cancels their chauffeur and picks them up, explaining the advantages of making movies. At home Gwen and Ernest find her little brother, mother (Lucile Watson), his uncle Sheridan Lane (Berton Churchill), Aunt Amelia (Kathleen Lockhart), and Augustus (Gene Lockhart). They all sing. Kay Jordan (Florence Rice) tells them of their full schedule. When Orlando Lane (Raymond Walburn) arrives with his company, Gwen and Ernest decide to go to Hollywood.
Press agent Dink Rogers (Allyn Joslyn) denies it. Gwen tries on new clothes. For radio Gwen sings "Summer Serenade." Ernest sings for the recording of "On Parade" and then rushes to the radio broadcast to sing with Gwen. Felix hopes they will come back to New York, but Trumpett calls him. Leo says they can be separated. Gwen and Ernest pack and sing "Home in the West." Leo reads his play to Gwen, quoting Ernest's romantic notes to a secret mistress. Gwen learns that Kay picked out Ernest's new suit, which she burns. Ernest tells Gwen he persuaded Kay to come to Hollywood. Gwen goes in Kay's room and finds a note from Ernest. Kay tells Ernest she will get it engraved for Gwen. Ernest wonders what is the matter with Gwen. Trumpett brings the contracts, but Gwen says she is not going. Ernest learns that Gwen is jealous of Kay. The show closes, and two separate shows go on the road. Gwen's mother reads her a review of Leo's failed play, and Gwen realizes she was fooled. Gwen and Ernest call each other and go to Felix, saying they are flying to Hollywood; but Felix gets them to stay in New York and perform in Sweethearts again.
This musical comedy reflects the differences between performing on Broadway or in the movies as the stars repeat their performance for a live audience daily but have little time to relax.