Adapted from Claude Anet's novelization of a true story, an Austrian prince falls in love with a mistress but is forbidden to see her again.
Prime Minister Taafe (Jean Debucourt) warns Emperor Franz Joseph (Jean Dax) about students and the editor Szeps, who visits Prince Rudolph. People are arrested, including Szeps and Rudolph (Charles Boyer). Rudolph assures his father he will wed Princess Stephanie only to produce an heir; but he has many women.
Five years later Rudolph drinks with soldiers. The Chief of Police (Vladimir Sokoloff) spies on him for Taafe. A gypsy woman sings to Rudolph and reports to the police chief. Rudolph knows that two policemen follow him. He rescues Marie Vetsera (Danielle Darrieux) from a pestering man and enjoys her company; she says he resembles Prince Rudolph. Rudolph tells Taafe to re-open Szeps' newspaper, but he refuses. Rudolph learns he can't see his father for 48 hours and attends the opera with him. He is seen by Marie and gazes at her, remembering her. Marie tells her nurse about Rudolph. In church Rudolph speaks to Marie. His cousin Countess Larisch (Suzy Prim) calls on the Baroness Vetsera (Marthe Regnier) and borrows her daughter Marie for an hour, taking her to the palace. Marie is not afraid of Rudolph, and he is surprised she doesn't ask for anything. Their visits are reported to Taafe, and the police chief writes to warn her mother. Marie tells Rudolph they have two hours and that she loves him. Although her mother scolds her, Marie won't say who her lover is.
Rudolph learns that Marie was sent to Trieste for a month, and he gets drunk and shoots his image in a mirror. Marie returns to find him ranting until her love calms him down; she loves him and won't leave him. Rudolph tells her he wrote to Rome for an annulment and gives her a wedding ring. She wishes to die before him. Her brother George gets upset when someone says she is with Rudolph; but the prince stops the quarrel by putting George under arrest. Rudolph visits George in jail and says he loves Marie more than anyone. Franz Joseph tells Rudolph the Pope refused his request and demands he give up Marie. Rudolph says he will abdicate; but his father says he must break it off in 24 hours or he will send her to a nunnery.
At a royal ball Marie sees Rudolph with his wife. He opens the ball by dancing with Marie, who says she will follow him anywhere, even from where one does not return. Rudolph presents her to his father, and he arranges for her to meet him at Mayerling at a hunting party. Marie asks Rudolph to choose the moment and not tell her. On January 30, 1889 Rudolph kisses Marie goodnight. Early in the morning he shoots her, tells his valet the shot was outside, and then shoots himself, grasping her hand and dying.
The liberal Rudolph was shut out of his father's conservative government over the Hapsburg empire, and evidence for the speculation that he was assassinated was found; suicide may have been used as a cover. The film presents the tragic story of two lovers who chose death rather than be separated by politics.