Mrs Anna Leonowens, a widow from Wales, arrives in Bangkok with her young son to teach English to the children of the royal household. The King very much wishes to absorb western knowledge, but is sometimes conflicted over how to reconcile western ways with Siamese culture. His efforts to do this, unadmitted even to himself, are further hindered by the Kralahome (Prime Minister), who wishes to keep western influences out of the court.

Meanwhile, a new slave for the King, Tuptim, who is a present from the Prince of Burma, befriends "Mrs Anna" and borrows her copy of Uncle Tom's Cabin. She transforms this into the Ballet "Small House of Uncle Thomas" which is presented to the visiting English Ambassador, Sir Edward Ramsay. The ballet makes clear her unhappiness with her lot, and after the show she attempts to escape in the company of her lover Lun Tha, the Burmese emissary.

When she is caught, she is dragged before the King. Anna pleads with the King not to whip her, but he states that he will do so as he is a "strong King". He finds however that he cannot bring himself to do so (presumaby as a result of Anna's influence) and he hides himself away and declines in health.

Anna, thinking that she can no longer be of any use, is just about to leave when she is told that the King is dying. She decides to stay in order to help his young son, Crown Prince Chululongkorn, her favourite pupil, to rule his people.