Vedachalam [T. S. Balaiah], a wealthy businessman from Ooty, is married to Sundari [M. S. Sundari Bai] and has a son, Ravi [Sivaji Ganesan], who now runs the family business. Vedachalam is also secretly married to Sivakami and has a daughter Vijaya [K R Vijaya] by the second marriage. After Sivakami's death, his daughter decides to seek him out and sets out to Ooty to confront him with proofs of the second marriage.
Meanwhile, another Vijaya, the daughter of a wealthy zamindar, enters the story. After her parents die, her uncle tries to marry her to gain her wealth. Unwilling to marry him, she runs away. On the way to the railway station, her taxi runs over the first Vijaya. The taxi driver refuses to help, but Ravi, who comes on the same road, spots Vijaya and ensures she is hospitalized.
The second Vijaya [L. Vijayalakshmi] reaches the railway station and realizes that she has the first Vijaya's luggage. She opens the trunk and finds evidence of Vedachalam and Sivakami's wedding. Needing a place to stay, she decides to go to Vedachalam and claim that she is his daughter. She meets Ravi on the train and pretends to be Vedachalam's daughter. Ravi is unsettled by the discovery that his father had a second wife, but does not reveal his identity to her.
The second Vijaya meets Vedachalam and confronts him. He accepts the charges and introduces her to his wife and son as his friend's daughter. Vijaya also agrees to pretend to be his friend's daughter. For the moment, Ravi accepts her claim, but soon realises that she is not his real sister because his sister is left-handed while Vijaya is right-handed. She is forced to tell him the truth.
Initially, Ravi decides to throw her out but later tells her to continue acting as his sister in order to spur his father to admit his deceit and accept his real daughter. Meanwhile, he falls in love with her and his mother accepts their relationship and desires to see them wed. Vedachalam is against the relationship since he believes that Vijaya is his daughter.
Having lost the proof of her birth, the now-recovered first Vijaya meets her boyfriend, Sundaram [R. Muthuraman], and seeks his help. Since his father is against love marriages, Sundaram shelters her in a hotel. Dr. Thirupathy [Nagesh], the family physician, spots a “Missing” advertisement placed by Vijaya's uncle and begins to investigate who she is. Meanwhile, Ravi meets his real sister in the hotel with Sundaram. Being Sundaram's friend, he helps the couple without revealing his own connection to Vijaya. On Sundaram's suggestion, Sundaram takes Vijaya home, claiming that she has lost her memory after the accident.
Sundaram’s father agrees to let them stay and eventually to arrange introductions to the family. Ravi explains to Sundaram’s father that Vijaya is Vedachalam's daughter and suggests a quiet marriage between Ravi and Vijaya because her wealth could ease the family’s future. Meanwhile, Vijaya hopes for Ravi's attendance at their wedding, but he reveals that he is already in a registered marriage with Vijaya on that day.
To hasten matters, Sundaram’s father promises to conduct both weddings together at his expense. A tense moment arrives when Thirupathy’s wife informs Vijaya's uncle of her whereabouts, and he kidnaps her on the wedding day. Thirupathy, Ravi, and Sundaram quickly intervene to rescue her and return to the venue.
Vedachalam arrives to attend Sundaram's wedding and is shocked to see Ravi also preparing to wed. Cornered, Vedachalam finally confesses that he had a daughter by a second marriage, and that Vijaya is that daughter. Ravi then steps forward and explains that she is not the daughter but Vijaya is. Sundari forgives Vedachalam, accepts Vijaya, and both marriages proceed to a joyful conclusion.
