Pratheesh and Treesa, the young couple, arrive to a beautiful village blessed with hills and rivers. They settle there in a rented room with the help of the villager Prakasan. Pradheesh makes a living by working as a painter in the company of Prakasan. Though the villagers come to like the young couple, they feel that there's something mysterious in Pradheesh and Treesa. Their suspicions increase when the couple frequently ask them the location of the river in the village. It is the rest of the story of the young couple that the film Thanuppu unravels in a tone of unflinching social commitment.