The Bavarian Castle of Possenhofen is all agog when Austrian Emperor Franz Joseph invites the young Duchess Helene of Bavaria, called Néné, to Bad Ischl for a closer acquaintance. Everybody expects that Néné will become the young Emperor's wife. But when in the process of getting to know each other the paths of Néné's fun-loving younger sister Sisi and the straight-laced Franz Joseph cross as well, things turn out differently: The two fall in love at first sight and the Emperor decides, against the express wishes of his mother, Archduchess Sophie, to marry Sisi. The tomboy is prepared for her future role at the side of the Austrian Emperor in a kind of crash course, and the couple celebrates a dream wedding. But even in the wedding night, Sisi urges Franz Joseph to escape the strict court protocol: They spend the night in the park of Schönbrunn Palace. Very soon, everyday life catches up with the the young couple. While Franz knows no other life than that of an Emperor, for which he had been raised since birth, the free-spirited Sisi feels smothered by the traditions at the Viennese court, so contrary to her own liberal upbringing. Especially Franz Joseph's stern mother Sophie is anything but enthusiastic about the young woman's unconventional behaviour. Doubtful that Sisi will ever become a good Empress for her people, Sophie appoints Countess Esterhazy as lady-in-waiting for Sisi, so she will be informed of each step the young Empress takes. Used to having her own way, Sisi rebels against the court etiquette, inciting admiration, but also astonishment and rejection, especially from the conservative nobility. To the Emperor's surprise, his liberal wife takes a political interest and exercises her influence, visiting orphanages and relishing the sympathy the people feel for her. Soon Sisi gives birth to her first child, a girl who is named Sophie after her grandmother. When her mother-in-law takes the child's upbringing in hand, Sisi leaves the court in protest and travels to her family in Possenhofen. There she is urged by Hungarian Count Andrassy to plead with the Emperor for reforms and greater autonomy for Hungary and the Italian provinces, but Sisi keeps her distance. Informed by Countess Esterhazy, Sophie demands Sisi's immediate return to Vienna. Franz Joseph actually has his young wife brought back to Vienna, but only so that she can travel to Lombardy by his side. It is due to Sisi's skills that a scandal can be avoided. A gala soiree in the Scala is attended not by the invited Milanese nobility, but by their servants. Sisi still insists on remaining in her loge and so wins the people's hearts. The birth of her second daughter is a mixed blessing to her mother-in-law Sophie. She reminds her son that the Empire needs a male heir to the throne. But Franz Joseph takes a stand and celebrates his daughter's birth with an amnesty for political prisoners. Soon after that, the Imperial couple prepares to travel to Hungary.

The loss of her firstborn daughter drives Sisi into a severe depression. She is sent to recuperate in her brother-in-law Max's Castle Miramare. Her daughter Gisela finally gives her the strength to face her duties once again. Back in Vienna, Max presents her with his fiancée, Charlotte of Belgium. The political situation is more critical than ever. Franz Joseph hopes for support against the rebelling Italian provinces from Napoleon III. Although Sisi doubts the French Emperor's sincerity, she hopes for peace: She is pregnant again. When Rudolf, the heir to the throne, is born, all Vienna celebrates with unbridled joy. But war is inevitable. Franz Joseph simply brushes his brother Max's objections aside and instead anticipates victory with France by his side. But he has miscalculated: Napoleon III sides with Lombardy. Sisi is treating the wounded in a military hospital when Count Andrassy once again approaches the Empress and prophesies that the Empire will break apart. When a defeated Franz Joseph returns to Vienna, Sisi demands he allow a Parliament to win back his people's trust in him. During a vacation in Possenhofen, the Imperial couple finds peace and relaxation. Back at the court in Vienna, though, there is an upset concerning the education of Rudolf, the heir. Backed by Franz Joseph, Sisi's mother-in-law Sophie plans a military education in the Hapsburg tradition for the boy. Meanwhile, Max leaves for Mexico, which has offered him the Imperial crown. He, too, had been brought up to reign, but now is constantly overshadowed by Franz Joseph, whose views he doesn't share. In the face of this sad farewell, Sisi demands from her mother-in-law to leave the education of her children to herself. But Sophie refuses: The Empire's future demands sticking to the principles. When Rudolf becomes estranged from her, Sisi herself fetches the delicate boy from the military academy, where he had been brutally disciplined; but Franz Joseph takes sides against her. Sisi collapses in a faint, her Physician diagnoses a severe pneumonia. The worst seems to be over soon, but Sisi has lost her will to live. In Venice she slowly recovers, but she won't answer Franz Joseph's passionate letters, as long as Rudolf has to stay at the military academy. Sisi's recovery progresses, so that she can attend a masked ball. Count Andrassy flirts with the young woman whose identity he doesn't know. When Sisi takes off her mask, he uses the opportunity for a confidential conversation: He doesn't feel this kind of trust to any other person besides the Austrian Empress. Sisi reminds him that her place is by her husband's side, even if, or particularly when, he is in error. Back in Vienna, Franz Joseph has finally realized that the harsh military education is threatening to break Rudolf. When Sisi begins her homeward journey, Franz Joseph and the children set out to meet her. The family celebrates a happy reunion.