Dui Bon' is the story of two cousin sisters Himani and Ulka. Ananda, an upcoming writer leaves his village to pursue his writing career in Kolkata. He rents a room in Mr. Bishwambhar Dutta's house. Ulka is Mr. Dutta's daughter and Himani is his niece. Ulka goes to college and pursues music while Himani is neglected and has to do the household chores. Ananda develops feelings for Himani. Ananda's book 'Jorer sanket' written under the pseudonym Gautam Basu gets good response from reader and Ulka falls in love with the writer. Ulka discovers a page written by Ananda an mistakes it for a love letter written to Himani. Ananda is thrown out of the house. After the release of Ananda's second book Ulka realizes her mistake. She also finds out that Ananda is actually Gautam Basu. Ananda and Himani's marriage is fixed. When Ulka finds out she tries to commit suicide but Kalipada's presence of mind saves her.