Ralahamy, a member of high status, dies leaving his family in debt after having squandered his fortune through extensive drinking and other vices. To get back into wealth, Ralahamy\'s wife Tackla pushes her daughter Ranjani to get married to a wealthy older man Victor with a child through an earlier marriage. In this process, Samson, Ranjani\'s boyfriend, who had tried extensively to get the family back into good graces going so far as to pay off their debts, is spurned. He then goes abroad to win a fortune.

When Samson returns he learns of Ranjani\'s engagement to Victor and tries to reach her through letter. His letters are hidden from her however, and rumours spread that Samson is now a cripple. Ultimately the truth is revealed.

Kadawunu Poronduwa (Sinhala, "The Broken Promise") was the first film to be made in the Sinhala language; it is generally considered to have heralded the coming of Sinhala Cinema. The film was produced and filmed in India however, and was highly influenced by South Indian melodrama. It was first shown on January 21, 1947 at the Kingsley Cinema in Colombo.

A remake was released in 1982.