Rajalingam is the only son of Ramalingam, the zamindar of Kalathur. Kannamma is the daughter of Murugan, a farmer from the same area. On the zamindar's advice, Murugan sends his daughter to Madras for higher education. While returning from Madras, Kannamma meets Raja on a train. Noticing her respect and awe for the zamindar, Raja pretends to be an electrician visiting the palace. They fall in love, and a few days later Kannamma learns the truth. To reassure her, Raja marries her secretly in a temple.
Two days later, Raja has to go abroad for higher studies. During his absence, Ramalingam learns of the marriage and orders Kannamma to forget his son. Moved by the zamindar's feelings, Kannamma promises never to mention their marriage to anyone. Ramalingam then arranges Murugan and the now-pregnant Kannamma to stay in a nearby town, Sevalpatti. Murugan, ashamed of Kannamma's secret marriage, leaves Kannamma's newborn son in an orphanage and lies that the child was stillborn. They both decide to leave the place and drift toward Bangalore.
When Raja returns, he learns Kannamma had left Kalathur. His inquiries in Sevalpatti lead him to believe that Kannamma led an immoral life. Grief-stricken, he travels from place to place to forget Kannamma and turns to drinking as a last resort. In Bangalore, he encounters Kannamma in a dancer's house where she had come to teach the dancer's daughter. Her presence in the house and her reticence to Raja's questions deepen his belief that Kannamma is a woman of ill repute, and in disgust, he returns home.
Kannamma's son Selvam grows up into an intelligent boy and lives in the orphanage in Sevalpatti. Murugan visits the orphanage and, upon meeting Selvam, decides to move to Sevalpatti to be near him. Kannamma becomes a teacher in Selvam's school and feels drawn to him. She invites him to stay with her, but he declines as he must look after Mani, a lame orphan living with him. Raja is invited to Sevalpatti by Singaram, a rich merchant who wants his daughter Maduram to marry him, to preside over a school function. Raja becomes fascinated with Selvam, who acts in the school play. After the performance, he encounters Kannamma again and orders the headmistress to dismiss her.
Mani is critically ill, and Selvam turns to Raja for help. Raja brings a doctor who cannot save Mani. Raja then takes Selvam with him to the palace. At Selvam's insistence, he stops drinking and, in order to give him a mother, decides to marry Maduram. A seriously ill Murugan confesses to Kannamma that her child is not dead and reveals Selvam's true identity. Kannamma tries to reach Selvam but cannot find him in the orphanage. The news shocks Murugan, and to soothe his nerves, they move back to Kalathur. In the local temple, Kannamma meets Selvam and tells him that she is his mother. On learning from him that Raja is bringing him up and plans to marry him off, she asks him not to reveal anything about her to Raja.
Maduram learns from Selvam that he is Raja's son, and Singaram insists on a written undertaking that Raja's properties would go only to Maduram's children. The news of this conflict spreads through the village. Hearing this, Murugan hurries to the palace to reveal the true identity of Selvam, but collapses near the gate. Kannamma follows and, as she tries to move away with Selvam, is intercepted by Raja, who demands the boy back. Raja refuses to believe that Selvam is Kannamma's son and insults Kannamma for her supposed shameless life. Ramalingam sees that, even in humiliation, Kannamma remains silent about her promise to him. He is deeply moved and acknowledges her as his daughter-in-law. In the end, Selvam is reunited with his parents, and Raja's marriage to Maduram is cancelled, setting the stage for a new, hopeful future.
