Based on S. N. Behrman's play, an aunt arranges for an orphan to be married to the mayor, but she dreams of a pirate and falls in love with an actor who impersonates the pirate.
Aunt Inez (Gladys Cooper) has arranged for orphaned Manuela (Judy Garland) to marry Don Pedro Vargas (Walter Slezak), and she accepts his engagement ring. Manuela begs her aunt to take her to the Caribbean Sea. Serafin (Gene Kelly) entertains at Port Sebastian, singing "Niña" to various women and dancing. Serafin asks Manuela who she is and says he loves her.
In his show Serafin hypnotizes Manuela, who says she loves the pirate Macoco and sings "Mack the Black." Serafin dresses as a pirate and kisses her. Manuela tells Aunt Inez that she wants to go home.
In her wedding gown Manuela tries to avoid Serafin, but he walks a tightrope and comes in her window. She tells him that she does not love him, but Serafin asks her to sing with his troupe. Don Pedro comes in and tries to whip Serafin, who calls him Macoco. Don Pedro is mayor and offers him money to keep the secret. Serafin has Don Pedro sponsor his players.
Serafin tells Aunt Inez and Manuela that he is Macoco. He postpones the marriage and takes control of the town. Manuela imagines him dancing around her with a sword. Serafin demands that the town send Manuela to him, and the Advocate (Reginald Owen) tells Don Pedro, who goes to get the militia. The Advocate asks Manuela to sacrifice herself. She goes to Serafin and says she despises actors. She throws vases and other things at him. When he collapses, she melts, sings "You Can Do No Wrong," and kisses him.
Don Pedro returns with the Viceroy (George Zucco), who orders the soldiers to surround Macoco. Manuela says that Serafin is pretending, and Serafin shows his passport; but Serafin's chest filled with jewelry is evidence against him. Manuela pleads to stop the hanging. She sees jewels in the chest that match her ring, and she glares at Don Pedro. The Viceroy lets Serafin speak. Serafin says he wants Macoco to hang, and Don Pedro tries to stop Serafin from speaking. Serafin presents a show. He sings "Be a Clown" and dances. Serafin starts to hypnotize Don Pedro, but Manuela appears hypnotized and sings romantically to Serafin. Jealous Don Pedro tells Manuela that he is Macoco and draws pistols; but he is captured.
In the final scene Serafin introduces Manuela, and they sing "Be a Clown."
This musical plays upon a woman's fantasy for a romance
with a pirate, but she finds the reality of a brutal pirate inferior
to the charm of an actor who can dance.