Assistant Engineer Mohan's (Sathyan) wife dies of snake bite when his son Babu is a teenager. The title cards are shown after this incident. So when the story opens Babu is a school going boy (This role is performed by Kamal Hassan). Mohan goes abroad on an official assignment and Babu is enrolled in a boarding school. Babu becomes lonely and homesick especially when he sees his classmates getting letters from their parents and when they come to meet them. Babu is made to believe by the old servant that his mother is in 'vaikuntam' (heaven). Babu sends letters to his mother addressed as "Mother, Vaikuntam". The letters are entrusted to the gardener Gopalan Nair (Muthukulam Raghavan Pillai) to be mailed. Gopalan Nair's daughter Sarala (Ambika Sukumaran) happens to see the letters. She takes pity on the child and replies to the letters as if sent by his mother whom he believes is in heaven. Through these letters, Sarala and Babu become close to each other. Once, Babu gets injured while playing. Sarala who meets the child for the first time nurses him until his wounds are healed. Babu believes that Sarala is his mother who has come from the heaven to nurse him and Sarala does not correct him. Mohan returns. He marries Sarala so that Babu may not lose her. Sarala gives birth to Indira (Baby Vinodini). She dotes on both as her own children. Gopalan Nair does not approve of his daughter's fondness for Babu. He reveals the truth to the boy. Babu is upset; he begins to feel that Sarala does not care for him. He runs away from home with Indira. Mohan and Sarala, with the help of the police, begin their search for the children. Babu and Indira are found on the top of a multi-storeyed building. In a risky rescue operation by the police the children are rescued. Babu comes to realise that though his mother is dead Sarala loves and cares for him. This was the first Malayalam film of Kamal Haasan - he played Sathyan's son. Vinodini was a child artist when she did this film and she did a dual role (child Babu and Indira) in this movie. The climax scenes of this film were shot on the top of the Sree Narayana Guru memorial at Varkala, Sivagiri.