Mela is set around a village fair held during Rash Purnima in a remote village of West Bengal. The fair brings together villagers, stall owners, performers and visitors, creating a temporary centre of social and economic activity.
Bishu Mama arrives at the fair with his nephew Ratan to run a food stall. Nearby, Brojomohan operates another stall with the help of his orphaned niece Alta, while Hriday and Kali sell earthenware. The fair also includes organisers and jatra performers, including Haradhan and Tarini Khuro. Various incidents involving the stall owners, visitors and performers unfold as the fair continues.
Ratan and Alta gradually develop a relationship while taking part in the activities around the fair. Their time together includes visits to an old temple, a deserted mansion and a pond near the fairground. Meanwhile, other events take place among the people gathered there, including disputes between stall owners, a child becoming separated from her family and the activities of a mentally disturbed woman who moves through the fair.
As the festival progresses, friendships develop and tensions arise among the people staying there. The jatra performances and songs become part of the atmosphere of the fair. After the celebrations end, the temporary stalls are dismantled and the visitors and stall owners leave, bringing the gathering to an end.