An American showgirl in London creates an international incident when she falls for a European prince.

In 1911, the Grand Duke Charles, Regent of the Balkan State of Carpathia, arrives in London to attend George V's coronation. With him are his mother-in-law, the Queen Dowager, and his sixteen-year-old son, King Nicolas VIII, who will succeed him as ruler in eighteen months. The British Foreign Office assigns the task of keeping Charles happy during his London stay to the Honorable Peter Northbrook, the Deputy Head of the Far Eastern Division who protests he knows nothing about Carpathia. Northbrook takes Charles, a widower, to see a musical show, where, backstage, Charles' introduction to chorus girl Elsie Marina proves memorable when her shoulder strap snaps as she shakes hands. That evening Elsie receives an invitation to a midnight supper at the Carpathian Embassy. After donning a carefully chosen white evening dress, she is escorted by Northbrook to the Embassy. Although expecting a large party, she discovers that Charles has planned a tryst in his private suite. Unwilling to participate, she tries to leave, but Northbrook, hoping to minimize Charles's disappointment, offers to "rescue" her later by pretending that a hospitalized aunt has called for her. Charles greets Elsie with trite expressions that she knows are preludes to seduction, but then excuses himself from the table and telephones the Carpathian ambassador. The neglected Elsie, becoming tipsy on vodka, bristles to hear him joke about naïve Americans protesting the arrest of dissenters in Carpathia, unaware that he is trying to prevent political upheaval that will lead to war. A brilliant strategist, Charles suspects that the Germans are politically courting the misguided Nicolas behind his back. Eventually Charles returns his attention to Elsie, but she evades his amorous advances and Nicolas enters, demanding to know the reason for his friends' arrest. Giving little explanation, Charles orders that Nicolas be locked in his room and barred from using the telephone. After a night out, the dotty and hard-of-hearing Queen Dowager also visits and takes a liking to Elsie. After she leaves, Charles resumes his awkward seduction. However, the drunk and giggling Elsie is uncooperative and tells him there is not enough love in his life. Surprised that he made no effort to be romantic, which she would have found hard to resist, she wishes him "better luck next time" with someone else. Offended, Charles rings for a footman to take her home and, stinging from her comments, scolds the servants for not perfuming the room, turning down lights and providing music. Eager to please, the confused servants carry out his ideas and Charles realizes that seduction is still possible. He tells Elsie about a sleeping prince waiting to be kissed back to life, and with a few more words and the help of a violin-playing valet, is on the brink of seducing her when Northbrook enters as planned and breaks the mood. Besotted, Elsie sends him away and warns Charles that she might fall in love with him, but then passes out and is carried to bed where she spends the night alone. The next morning, on the day of the coronation, Elsie awakens and realizes she has fallen in love with Charles, who is anxious to get rid of her. She agrees to make a telephone call for Nicolas and eavesdrops as he, speaking in German, arranges for the Bulgarian Army to overthrow his father. Afterward, she confesses that she knows German, but is ambivalent about whether to reveal his plans. Seeing Elsie in the hall, the Dowager appoints her lady-in-waiting for the coronation and accessorizes her gown with jewels and headgear. For further adornment, the Dowager insists that Charles invest Elsie with a Carpathian order, so that she can wear a medal. While riding in the open carriage to the coronation, Elsie waves gleefully to her friends, amusing the usually stern Charles. Upon returning to the embassy after the lengthy ceremony, Charles confronts Elsie and Nicolas about the phone call. When Nicolas refuses to divulge the particulars of the call, Charles forbids him to attend the coronation ball. After Nicolas leaves the room, Charles expresses concern about him, but dismisses Elsie's suggestion that "he needs more love." Acting on Elsie's advice that Nicolas might be more cooperatvie if Charles were less strict with him, Charles permits him to go to the ball. Having no one to accompany him, Nicholas refuses unless he is allowed to invite Elsie, who accepts to be near Charles. Nicolas then promotes her to a first-class order and gives her the appropriate medal. At the ball, Charles invites Lady Lucy Sunningdale to a midnight supper and then searches for Nicolas and Elsie, whom he asks to dance. While waiting for the music to start, Elsie again tries to reconcile father and son. Concerned that he is beginning to enjoy Elsie's company, Charles abruptly arranges to send her and Nicolas home. Later at the embassy, Northbrook tells Charles that Elsie is teaching Nicolas to foxtrot. When Elsie sees the dinner table meant for Lucy, she assumes it is set for her. To spare Charles embarassment, Northbrook offers to escort Lucy to a different room when she arrives and fetch him on the pretense that the ambassador has called. Before the plan can be implemented, however, Elsie shows Charles a letter from Nicolas, proclaiming support of his father, which Nicolas will make official if Charles agrees to several conditions. While Charles considers his response, Elsie, who sees his loneliness, becomes romantic. From the hallway, the valet, leading a small orchestra of servants, plays music to which Elsie sings about love. Warming to her, Charles says he longs for that kind of freedom, and recites a poem. Each proclaims love and as they embrace, Northbrook enters, but Charles orders him to leave. The next morning, Nicolas reports to Northbrook that Charles called him "darling boy," and asked if he had enough love. Northbrook, too, finds Charles happier. Although the royal family must depart that day, Charles plans to care for Elsie financially and asks Northbrook to assist him with the details. Charles tells Elsie that he will be turn over his throne to Nicholas in eighteen months and she says her contract with the theater will end at that time, leaving them both free. However, they acknowledge that a lot can happen in eighteen months. The Dowager, seeing Elsie in the same white dress, suggests that she vary her apparel occasionally. After watching the royal family depart, Elsie collects her belongings, takes a last look and leaves, wearing a borrowed raincoat over her white evening gown.