The time is the early 1860's. The place, the royal capital city of Bangkok in the kingdom of Siam. Anna Leonowens, an attractive English widow, arrives in Bangkok with her son Louis. She has been engaged by The King of Siam to teach English and other Western ideas and philosophies to members of the royal family, including the king's many wives and many more children. Escorted ashore by the King's Prime Minister, The Kralahome, Anna is unsure that she has made the right decision by coming to Siam, but decides, for now at least, to abide by her end of a bargain with the King.

In the King's court, attempts toward implementing Western values clash with old fashioned customs and traditions. Even as the King is proclaiming his belief in the ideals of the West, he accepts a gift from the King of Burma - a peace offering, a slave. The King admires the young girl, Tuptim, not suspecting her lack of interest in him nor the fact that her true love is Lun Tha, the young Burmese who has escorted her to Bangkok.

Anna is finally presented to the King, and her doubts turn to indignant anger when it seems that His Majesty has a cavalier way of forgetting issues that do not interest him - such as Anna's salary, her days off and the issue of a brick house that was supposed to be built for her adjacent to the Royal Palace. But, on the verge of storming out, Anna is coaxed into meeting the Royal Children. She is introduced to the King's first wife, Lady Thiang, and in turn to the King's children. So taken in is she by the children, that she decides to stay on and teach.

In the classroom Anna instructs the Royal Children, the King's wives and sometimes the King himself. They learn of a great outside world where there exists such strange unheard wonders as snow, ice, and freedom of the individual.

When the King learns that a British diplomat, Sir Edward Ramsay, is on his way from Singapore to Bangkok, ostensibly to pay his compliments to the King but also to assess the monarch's hold on his own throne, Anna cleverly finds a way to help the King convince Sir Edward that he is a sophisticated and commanding leader. Anna suggests that the King host a dinner for Sir Edward in the European style, with his wives dressed in the latest fashions, and with entertainment provided by the quick and intelligent slave girl Tuptim.

The King is so happy with the thought of this forthcoming dinner, and recognizing the friendship that is growing between himself and the equally strong-willed "Mrs. Anna," he now promises Anna that according to their agreement, he will get her a brick house.

The dinner proves a great success, despite the discomfort and anger that arises from the King during Tuptim's presentation of The Small House of Uncle Thomas, in which Harriet Beecher Stowe's passionate denunciation of bigotry in America, Uncle Tom's Cabin, has been transformed into a Siamese ballet. Nevertheless, the troubled mood of the moment is quickly forgotten in the warm and encouraging endorsement of his regime that the King receives from Sir Edward.

The plan has worked. Alone in the ballroom now, congratulating each other on the evening and reliving its finest moments, Anna and the King bask in their friendship. He recalls, from earlier in the evening, the strange Occidental custom of a man dancing with his arm around a woman's waist. The King persuades Anna to teach him the English dance and it becomes apparent, as they dance the polka, that there exists a strong attraction between them.

The mood is shattered by the startling news that Tuptim and Lun Tha have escaped together from the Royal Palace. They are discovered by the King's secret police; Lun Tha is killed, and Tuptim is captured and returned to the Palace. Outraged, his pride wounded, the King is prepared to punish her himself; his arm is upraised, the whip in his hand, he is ready to lash punishment across her back when Anna intervenes. She begs the King not to throw away everything he has achieved by this brutal act, and in her rage accuses him of having no heart at all. Angered, hurt but also unable to make Anna back down, the King instead drops the whip and, confused at his own actions, runs from the room. Anna realizes that she has so humiliated the King that she can no longer remain in Siam. Her belongings are packed and placed aboard a ship. As she is about to embark, she receives a note from the King, who is dying. The note expresses his gratitude for all that she has done for him. Tearfully Anna returns to the Palace to see the King.

Lying near death, the King is surrounded by his wives and his children. When they see Anna, the children embrace her and beg her not to leave. Anna is deeply moved and realizes how much she loves them and how much they need her. Dying, the King directs Anna to take notes from Chululongkorn, the new King. The Prince, who has learned his lessons well, regally announces that henceforth there will be no servile bowing and scraping before him. As the King dies, Anna, the Kralahome, the wives and children sink to the floor in a low curtsy and bow, in final obeisance to the dead King, and with respect for the new one.