Padmanabhan master and his wife Devaki are waiting for Unni, their only son who has been missing for many years. Ten-year-old Unni gets lost in the crowd during a temple festival where he went with his neighbour, Panicker , popularly known as Poorappanikkar. Panicker too did not go back to the village as he decided to return only after finding Unni. Panicker's daughter Ammu also believes, like the Padmaabhan and Devaki, that her father will return one day with Unni. The master publishes a photo made by an artist based on assumptions of older Unni in the newspaper. He finds his son after years at Nagappattinam and brings him to the village. Soon, the villagers realises that Unni is abnormal and mentally challenged. He behaves like a small boy and creates all sorts of trouble to the villagers and his parents. His main hobby is to snatch mundu from people. This leads to a series of comical incidents in the village.
He is given Ayurveda treatment under the guidance of the church priest Fr. Stephen. Ammu looks after Unni, to which her cousin Gopikkuttan objects, as he loves her. Meanwhile, Panicker returns to the village. Gopikuttan tries to turn Panicker against Unni. Eventually, Ammu falls in love with Unni and waits for his recovery to marry him. Finally, during a fight with Gopikkuttan, Unni tries to save him by holding onto his mundu when Gopikkuttan is about to fall off a cliff. Unni gets his memory of his past back and reveals the truth to Ammu that he is actually Vishnu, the son of a Bangalore underworld gangster Maheshwaran Thampi.
Vishnu disapproves of Thampi's lifestyle, and lives separately from his father. He falls in love with Gauri, an orphan girl and decides to marry her against his father's wishes. Vishnu and Gauri's friends arrange a secret party for them. Thampi learns about the party and its location. His men attack the place, and during the commotion, Gauri falls down even though Vishnu tries to save her. Due to this, Vishnu lost his memory and became mentally challenged.
In the present, Thampi visits Vishnu and asks him to come home. Vishnu refuses initially but agrees to go along after Padmanabhan Master asks him to do so. At his home, Thampi tells Vishnu that he realised his mistake and for the mistakes he made, Vishnu and Gauri were the ones who were punished. Thampi informs him that Gauri is not dead but is bedridden. Before her death, she wanted to meet Vishnu as her last wish which Thampi fulfills. Gauri asks Vishnu to marry Ammu and to bring her to Gauri. The film ends with Vishnu marrying Ammu, and Krishnankutty, Unni's friend and a village tailor, snatching his dhothi.
