International banker Richard M. Gresham brings Princess "Zizzi" Catterina of the small kingdom of Taronia to New York, hoping that publicity will inspire the U.S. to back a bond issue of $50,000,000 to help bring Taronia into the modern age.  Gresham's fervent opponent is handsome newspaper publisher Porter Madison, III.  When the princess comes down with the mumps and is quarantined for a month, Gresham hires look-alike Nancy Lane, a starving third-rate actress to play the part of the Princess for thirty days for $10,000, and an extra $5,000 if she changes Porter's opinion.

As the princess, Nancy bestows all her attention on Porter, and Porter becomes infatuated with her and shows her the city.  One night, Donald Spottswood, one of Nancy's fellow actors recognizes her and, when she fails to respond to him, starts to harass her.  After Porter hits the actor, he and Nancy leave, both in love with each other.

The next day in court, Donald demands that the man who hit him be found, and detectives sent to Nancy's apartment discover that she is missing.  The news makes the headlines, and fearing a connection between herself and the Princess will be made, Nancy goes to Porter's office as herself, but more rough around the edges.  Porter is convinced her story is genuine, but his reporter is not.

The Princess' publicly obnoxious fiancée, Count Nicholaus, then arrives as Nancy, still posing as the Princess, is about to leave on a cross-country goodwill tour.  His presence ruins Porter's hopes of marrying the Princess, as he believed he was the only man in her life, and Porter angrily leaves her.  Nancy refuses to allow the Count to tour with her, and the bewildered Count tells Porter's reporter that she is not the Princess.

Nancy's return to New York marks the end of the princess's stay in the United States, and Nancy and the Princess meet for the first time and become friends.  A final reception is held.  The King of Taronia arrives, having been summoned by the suspicious reporter, but the Princess handing out medals to Gresham and Porter is the real Princess, and any hint of scandal is squelched.  The King, angry that Count Nicholaus fueled the suspicions of the reporter, breaks the engagement, which delights the Princess.  The Princess advises Porter that although he may have been duped, Nancy is truly in love with him, and if she had been the real princess, she could never have married him.  Porter returns to Nancy, who tears up the check Gresham gave her and readily accepts Porter's embrace.

Notes
The film is Based on the story "Thirty-Day Princess" by Clarence Budington Kelland in Ladies' Home Journal (July - December 1933).

A news item in DV indicates that although production was slated to begin on February 28, 1934, it was delayed due to the illness of William Collier Sr., who was to play the "Managing editor."  Collier was replaced by Robert McWade. In his autobiography, Preston Sturges remarks that he and producer B.P. Schulberg disagreed on the writing credits for this film.  According to Sturges, Schulberg "as a producer, was accustomed to accepting praise for pictures as generals accept praise for the valor of their soldiers, and it thus seemed logical to him that the writers should feel the same general sense of shared accomplishment."  Sturges adds that although he shared credit with three other writers, "not much" of his work was used.