Russian prince goes to Monte Carlo just after World War I with money supplied him by Parisian Russians. He wins but the casino operators want him honor the tradition of returning to the tables.

Paul Gallard enters the grand casino at a sporting club in Monte Carlo with an empty suitcase and proceeds to win ten million francs at the baccarat table before the bank surrenders and closes for the night. Paul fills the suitcase with bank notes and the next day announces he is leaving that evening. Upset that he has been quoted in newspapers stating that his win was a miracle that could never happen again, the management thinks that their business will suffer and try to entice him to stay. He is offered the royal suite and the use of a yacht, and they arrange for him to bump into a hunchback, a sign of luck, and to be given a flower with three four-leaf clovers by a flower girl. Paul tosses the flower away, and it lands inside a horseshoe. When he pays no attention to these lures, the management vows that Paul must return and eat his words. On the train to Paris, Paul overhears a man tell an attractive woman about the beauties of Switzerland, where they plan to go after a connection in Paris. Upon returning to Paris, Paul goes to the kitchen of the Cafe Russe, where he divides his winnings with his fellow Russian refugees who had staked him. Paul is actually a former Russian nobleman reduced to driving a taxi in Paris for the past ten years, and he now vows to kill his gambling habit. He boards a train for Switzerland with his former servant Ivan and arranges for the woman whom he saw on the train to Paris to be mistakenly put into his compartment. He learns that the woman is Helen Berkeley and that the man traveling with her is her brother Bertrand. In Switzerland, Helen refuses Paul's many attempts to send her flowers and an invitation to dance; however, while climbing the Alps, Helen falls to a ledge where Paul has stopped. Soon they are riding together and dancing, and she confides in him that she is to be married in a fortnight to a sixty-two-year-old banker because Bertrand needs five million francs. Paul offers to share his Monte Carlo winnings, but she tearfully refuses and asks that he take her away so that they can spend a week together. Paul then ruefully accepts her request that they go to Monte Carlo. Ivan suspects that Helen has been hired to lure Paul back to the gambling tables, and Paul tells her that he would still love her even if Ivan were right, but that something inside would die. Helen actually had been hired by the casino management but since has decided not to go to Monte Carlo. She now confesses to Paul that she loves him, but refuses his marriage proposal. Helen then tells Bertrand that she is quitting despite his reminder that she was only a back street music hall performer when they were hired and that they will be paid 250,000 francs. When Paul tells Bertrand that he wants to marry Helen, Bertrand, to trick him says that she left already for Monte Carlo. While Paul and Ivan drive there, Bertrand tells Helen that they have left. She then changes her train reservation from Paris to Monte Carlo. Upon her arrival, Helen calls Paul's room to stop him from gambling, but Ivan reveals that Paul has already left for the club. Although Paul loses at first, when he is down to his last note, he begins to win. However, when the bank puts up its last tray of chips, worth six million francs, Paul loses. He laughs it off, but seeing Helen coming out of the director's office, he bitterly congratulates her and walks off. One year later, Paul, once again a taxi driver, drops off a passenger at a nightclub where he sees Helen's picture displayed. He gets dressed in tails and attends, and after Helen's song, dances with her and insults her, but then regrets it. Helen follows him and, finding out that he's a taxi driver, rejoices because she says that if he had lots of money, she could not tell him how sorry she is. She confesses she loves him, and together they attend a dinner and dance at the Cafe Russe in commemoration of Czar Nicholas II's birthday.