Set in 1939, the early days of World War II in Siam, the film begins with Angsumalin meeting for one last time with her childhood friend, a young Thai man named Vanus. He is leaving for England for schooling, and hopes that Angsumalin will wait for him and marry him when he returns.
Shortly thereafter, Thailand is invaded by Japanese military forces. In Thonburi, opposite Bangkok on the Chaophraya River, the Imperial Japanese Navy establishes a base. The forces there are led by Kobori, an idealistic young captain. One day he sees Angsumalin swimming in the river and falls for her. She, being a proudly nationalistic Thai woman, despises him because he is a foreigner.
Nonetheless, Kobori persists at seeing her and a courtship develops. Angsumalin finds that Kobori is a gentleman and starts falling for him, but she kept her feelings secret because of the war and because of her involvement with the resistance.
Then, for political reasons, Angsumalin's father - who is the leader of the Free Thai resistance, insists that she marry Kobori. Understanding that Angsumalin is not marrying him out of love, Kobori promises not to touch her, but he breaks that vow after the wedding.
Despite this, Angsumalin develops tender feelings for Kobori, but is still torn by her feelings for her nation and feeling guilty towards Vanus, upon whose return sets in motion a conflict between the two men.