Balu Thevar (Sathyaraj) and his wife Pechi (Saritha) belong to the Thevar community. He is an atheist, openly speaks against the caste system, but is tolerated by the villagers because of his helpfulness. His only son Sankarapandi (Raja) returns from the city after completing his education. He meets Vaidehi (Amala), daughter of a Brahmin, Neelakanda Sastri, or Sastri (Charu Hasan) and they fall in love. One night, they meet secretly inside the temple. Krishna Iyer (Janakaraj) comes there at the same time and suspects that someone is hiding inside. He locks the door outside and calls the villagers. Balu Thevar, as the village head, also enters the temple (for the first time) to catch the thief
Sankarapandi and Vaidehi try to escape and Vaidehi's anklet falls down, which is noticed by Balu Thevar and understands that there is a girl inside. Sankarapandi hides Vaidehi inside the sanctum sanctorum comes out and declares that he came to steal. The villagers also notice an idol missing (incidentally stolen by a thief at the same time). Though Balu Thevar feels that Sankarapandi is lying, he accepts Sankarapandi's confession and the villagers leave.
The next day, Balu Thevar agrees to compensate for the stolen idol. Balu Thevar, though upset about his son getting a bad name, appreciates him for protecting the modesty of his girlfriend. Balu Thevar meets Sastri and seeks Vaidehi's hand for his son, but is rebuffed and rejected by Sastri. Sastri learns from Vaidehi that she also loves Sankarapandi and about the temple incident. Sastri, worried that his daughter may opt for an inter-caste marriage, decides to get her married to a Brahmin in a neighbouring village. On the day of the marriage, by pretending to have drowned in the river en-route to the marriage venue, Vaidehi creates the impression that she has committed suicide. She hides in a forest ranger's ('Nizhalgal' Ravi) house. Sastri confronts Sankarapandi at a cliff and accuses him of Vaidehi's death. During this confrontation, Sankarapandi accidentally falls and hangs from a rock. When Sastri tries to save him, both of them fall down from the cliff and die.
Balu Thevar is shocked and saddened by their death. With the death of his father and sister Shankaran (Master Dhasarathi), a devout scholar of Vedas, becomes an orphan. He is considered inauspicious by his caste people, since his mother, father and sister have all died after his birth. He wanders the village streets, begging for food from his relatives. Balu Thevar gets worried on seeing this. Having lost his own son, he brings Shankaran home to raise him as his own son. Balu Thevar and Pechi stop eating meat and raising domestic animals at home for the sake of Shankaran's comfort. However, since Shankaran is living in the home of a lower caste person, his community people prevent him from learning Vedas.
Balu Thevar makes fun of Shankaran, telling him that it is not important to learn Vedas or to worry about caste. Shankaran now highlights Balu Thevar's hypocrisy, since he includes his caste (Thevar) whenever he mentions his name. After this, Balu Thevar stops using his caste name and uses his name only as Balu. He also throws all his community symbols (weapons) into the water and leads a simple life.
Vaidehi, not knowing of Sankarapandi and Sastri's death, informs the forest ranger about her lover and he promises to reunite them. On coming to the village he is shocked when he learns what had taken place. He returns and informs Vaidehi about the happenings. Vaidehi returns to the village to meet her brother and after meeting him, requests Pechi to take care of Shankaran for the rest of his life, and prepares to leave. Just then, Balu arrives and asks her to stay back as their daughter, though she should have been their daughter-in-law; Vaidehi agrees.
Meanwhile, Krishna Iyer, who was keen to marry Vaidehi and was insulted once by her, notices Vaidehi's return to the village. He cunningly instigates the villagers that her stay is extremely inauspicious for the village, since her last death rites had already been performed and that it is not proper for Brahmins to live in a non-Brahmin's house. The villagers start believing him; using this opportunity, they assemble before Balu's house and demand that Balu should send her out. Balu refuses, stating she is like his daughter and will protect her. The angry villagers decide to throw Vaidehi out on their own, but Balu stops them without any weapon and a fight begins. Some villagers who are already against Balu use this opportunity and stab him to death. Everyone is shocked by his killing as he has done so much good for them. Before dying, Balu makes his final request to the villagers to live in unity, and not to allow caste to divide them.
[from the book Pride of Tamil Cinema: 1931 to 2013, by G Dhananjayan, Blue Ocean Publishers, 2014]