During a train journey, Raja (Gemini Ganesan), son of rich estate owner Ramalingam Pillai (T. S. Balaiah) meets Kannamma (Savithri Ganesan), daughter of a poor peasant Murugan (S.V. Subbiah) working for his father, and they fall in love instantly. Initially, Kannamma is unaware of Raja's background. When she finds that he is her estate owner's son, she hesitates to reciprocate Raja's love. But Raja persuades her. They both marry secretly at a temple and live together for a while before Raja's father sends him abroad for higher studies.
Ramalingam comes to know about Raja's secret marriage to Kannamma and disapproves of it, as he wishes Raja to marry Mathuram (Devika), the daughter of another rich landlord. He persuades Kannamma to withdraw from the relationship and threatens to commit suicide if she doesn't. Being a girl of good character and daughter of a loyal worker, she promises to withdraw and continues to live with her father.
On learning that Kannamma is pregnant, her father gets angry and attempts to kill her. Ramalingam intervenes and advises them to migrate to another village until she delivers. She delivers a son but her father lies to her that the baby was stillborn; he leaves the boy in an orphanage run by Ramalingam. Kannamma and her father relocate to Bangalore where she works for a living. Her son Selvam (Master Kamal Haasan) grows up in an orphanage and studies in a local school. Raja returns to India and he is given wrong information about Kannamma's character. A disturbed Raja starts searching her, and unable to forget her becomes a drunkard. Once he visits a dancer where he notices Kannamma (who had come to teach the dancer's child).
Raja, who had now disbelieved the wrong information he had heard about Kannamma, misconstrues her presence there to mean that she is following immoral activities; he accuses her of spoiling his life. She tries to explain, but he doesn't listen. Disturbed by this turn of events, Kannamma and her father come back to the same village where Selvam lives; she works in his school as a teacher and they bond well with each other, not knowing their true relationship. A bright Selvam becomes the cynosure of all eyes. Raja, who meets Selvam in the Annual School Day celebration, decides to adopt him and takes him home. He also agrees to marry Mathuram under pressure from his father and all arrangements are made. On the wedding day, Mathuram and her father learn about the adoption of Selvam; they accuse Ramalingam of a conspiracy and throw Selvam out. Mathuram's father confides to his crony that he plans to acquire Ramaligam's properties through this marriage; Ramalingam overhears this and is shocked. Kannamma learns from her father that Selvam is her own son and comes to take Selvam with her. Raja abuses her before the gathering, but she maintains a dignified silence. Ramalingam realizes Kannamma's true worth and confesses his grave mistake of asking her to move away from his son's life; he accepts Kannamma and Selvam into his family and Raja is happy to join his estranged family.
(from the book Pride of Tamil Cinema: 1931 to 2013 by G Dhananjayan, Blue Ocean Publishers, 2014)