Zamindar Sivalingam (Sivaji Ganesan) is married to Lakshmiammal (Sowcar Janaki) and takes his family's prestige and heritage very seriously. Dancer Sulochana and Lakshmiammal have baby girls at the same time in the same hospital.Sivalingam is not in town at the time of the delivery and his close friend Ramaswamy (V. K. Ramasamy) takes care of Lakshmiammal. When the babies are taken for cleaning by the nurses, there is a short circuit and both nurses die. There is no way of identifying the babies. Sulochana who was abandoned by her husband, leaves the hospital. The doctor (Thambaram Lalitha) brings both babies to Lakshmiammal and she is not able to identify her baby either.Sivalingam arrives and seeing both babies in the room assumes he has twins. Knowing how important the family line is to him, Lakshmiammal, Ramaswamy and the doctor don't tell him the truth. Both girls, Chandra (Vijayakumari) and Kantha (Pushpalatha) grow up as the zamindar's daughters. Sulochana's brother, Nadaraj (M. R. Radha), who comes to know that his niece is growing up in Sivalingam's household and faced with the same confusion, takes up Lakshmiammal's offer and stays on there as a caretaker. Meanwhile, Lakshmiammal and Ramaswamy's wife, Parvathi (Radha Bhai), who are childhood friends promise to get their children married to each other.Chandra has a birthmark which is said to be very lucky but is by nature more like her Lakshmiammal. Kantha is more like Sivalingam. Chandra falls in love with her classmate Shekar (R. Muthuraman). Since he is the son of his wealthy friend, the late Mohanasundaram, Sivalingam agrees to the wedding.Ramaswamy, who lives lavishly and who is careless is his business matters, faces severe business losses and approaches Sivalingam for to back him in business matters. Sivalingam promises to give him money but refuses to let him use his name or claim his acquaintance. He also gives a job to Sundaram (A. V. M. Rajan) in one of his factories but refuses to have any further contacts with their family.When Ramaswamy and Parvathi hear that Chandra's engagement is fixed, they attend the function uninvited. Sivalingam insults them and Ramaswamy is driven to reveal that one of his daughters is not his own. The doctor mwho was also preseent there needs to confide too. The engagement is stopped and the family is thrown into confusion. Due to this, Shekar's mother (Rukmani) forces him to leave the place.Sivalingam refuses to talk to his family or the children and becomes extremely disturbed. Chandra tries to find a solution to this problem by leaving the house. She gives a lady called Maragatham her ring to act as the dancer Sulochana. Maragatham goes to Sivalingam's house and says that her daughter can be identified by means of a birthmark.The police arrive with some jewels and a suicide note from Chandra and they realise that she is now dead. Sivalingam is very happy when he finally becomes convinced that Kantha is his real daughter and fixes her marriage with Shekar. Lakshmiammal is very disturbed because she believes that all the confusion in the house was caused because they did not keep their word to Ramaswamy and Parvathi and get one of the daughters married to Sundaram.Kantha wants to humiliate Sivalingam, whose conceit caused Chandra's death and she made Lakshiammal practically bedridden. She refuses to marry Shekar and says that she will marry Sundaram. Meanwhile, Nadaraj who was thrown out of the house by Sivalingam traces Maragatham through the ring that she tried to pawn and the family is again thrown into confusion.Meanwhile, Chandra who attempts suicide by jumping into a river is saved by the inmates of an ashram. They persuade her to stay on as a teacher to the orphan students and she agrees. Shekar who is now an Education Inspector comes to the school and sees her. The principal (S. R. Janaki) however convinces him that she is an orphan girl who always lived in the ashram.Shekar then narrates the story of Chandra and also tell the principal that her sacrifice was wasted because Maragatham confessed the truth. He also tells her that both Sivalingam and Lakshmi are bedridden and that Kantha is struggling to care for both parents. Chandra wants to go back home but makes up her mind to move away instead. She requests for a transfer. Nadaraj overhears the principal and Chandra talking and is realises that Chandra is alive. He tells Sivalingam and Lakshmiammal and they set out in search of her.Chandra's taxi hits Sivalingam and he is admitted in the hospital. Both daughters give him blood and he understands that character is more important than family. Chandra marries Shekar and Kantha marries Sundaram.
Output: Question: Whose death causes the baby mix up?, Answer: Nurses