It's 1862 and English school teacher Anna Leonowens (JODIE FOSTER) has arrived in Bangkok to teach the fifty-eight children of King Mongkut (CHOW YUN-FAT), the ruler of Siam. At first, things are a bit tenuous for Anna in her new position. While her son Louis (TOM FELTON) seems to have no problem adjusting to this foreign culture, Anna is upset that the promise of a house for her and Louis outside the palace has been broken and that the King has yet to meet her some three weeks after her arrival.
Thus, Anna storms in to see the King, breaking all protocol and tradition and horrifying the monarch's advisors such as The Kralahome (SYED ALWI). Nonetheless, the King is somewhat impressed by Anna's tenacity and decides that she might be a worthy educator for teaching his children, including the heir to his throne, Prince Chulalongkorn (KEITH CHIN), about the ways of the Western world.
Mongkut is worried about his country falling behind the rest of the world and wishes to turn it into a major power by becoming as westernized as possible while still retaining Siam's traditions and culture. One of those is having many wives, and he's recently received a new one, Tuptim (BAI LING), into his fold, who's greeted by his main wife, Lady Thiang (DEANNA YUSOFF).
Even so, the King has more pressing concerns, what with recent attacks by neighboring Burmese soldiers on his people. Since Burma is controlled by Britain, Mongkut worries about that country's imperial ways, and his military advisors, including Prince Chowfa (LIM KAY SIU), his brother, and General Alak (RANDALL DUK KIM), urge that he take swift military action to quell the problem.
As Mongkut ponders over how to protect his country and its traditions while trying to bring it up to modern standards, he and Anna discover things about themselves and each other as romantic feelings begin to bud between the two.