The movie begins with a marriage scene in which the bridegroom disagrees to marry due to non-payment of dowry by the bride`s father. In spite of his brother's request, he remains stubborn. He even throws away the garland. Raja(Prosenjit Chatterjee) comes to the scene and tries to convince the bridegroom to marry. A challenge for test of brotherhood befalls Raja calls his two brothers Rana (Lokesh) and Rakesh(Abhishek Chatterjee) and orders them to drink poison. They gladly do so. It is revealed that the water in the glass contained honey instead of poison. The groom apologises and agrees to marry. All three brothers are worried about their only sister-Pooja's (Moumita) marriage and life. But Pooja convinces them to marry. All of them visit Anjali`s house and the marriage is settled. Nahim Ghoshal (Dulal Lahiri) buys a crown for goddess Lali made of pure gold which he wishes to offer for the god. He is stopped by Rakesh and a crash takes place. Mahim Ghoshal is insulted and agrees to take revenge. Raja later drives to Mahim's house for apology on behalf of his brother. Ghosal cleverly places a proposal of marriage between his son and Pooja. Raja ignorantly agrees; as a dowry Mahim Ghosal makes Raja transfer all his property in the name of Pooja, there by making them beggars. The film advances with the display of repeated insults and plans by Mahim Ghosal towards Raja's family as revenge. He even plots to create mental tension among the family members of Raja's family. But strong bondage and dedication among the three brothers prevents the fury. On the other hand, Mahim Ghosal and his son torture Pooja brutally, but keeping Pooja`s future in mind, Raja forgives them repeatedly. Pooja is expecting a baby but her husband even tries to destroy it. There is a clash and Raja, Rana and Rakesh carry Pooja to the hospital. Pooja has a boy. Mahim Ghosal and his son apologises at the hospital. They are forgiven and they live together ever after. The title Kartavya is suitable as it reflects the duty of a brother towards his sister.
Prosenjit Chatterjee as a Sobuj loves a next door girl Rachana Banerjee as a Saathi. But eventually Sathi turns out to be his friend Rahul's lover. Sobuj does everything to protect his friend's(Abhisheek) love. He loses his mother and his family. Facing bitter circumstances Rahul learns the lessons of life. He learns to work on his own and take responsibilities. After 2 years Rahul comes back but only to settle his sister's life. Again Sobuj comes to the rescue. He agrees to marry a neural patient to salvage his friend Rahul's love. But destiny played otherwise. Rahul had to marry a girl to salvage her sister's marriage. Sobuj did everything for Sathi but did not tell that he loved her. In the end Sobuj's mother did not tell . And what else, alls well that ends well.