Savithri (P. Bhanumathi) and Seetha (Sowcar Janaki) are daughters of a rich man in Chennai. While Savithri marries a lawyer (S.V. Ranga Rao) and is well-settled, Seetha loves and marries a worker Munusamy (TS. Muthiah) and lives in poverty.
Savithri has two stillborn pregnancies and the doctor tells her that she cannot have a baby and she is shattered. Seetha delivers a boy and struggles to bring him up. Understanding their financial difficulty, Savithri requests Seetha to allow her to bring up the child, but she refuses.
Soon, unable to solve their sudden and big financial crisis, Seetha and Munusamy decide to give their child to Savithri in adoption. Savithri gives them the money and makes Seetha swear to never claim her son back. Seetha and Munusamy leave to Rangoon (Burma) on work.
20 years roll by and Savithri is highly attached to her son Selvam (Raja) and shields him from even the smallest problems. She also brings up her relatives Sarasu (Kumari Saraswathi) and her father, and Dayanidhi (Chandra Babu) whom she brings up as her brother. Selvam and Sarasu like each other. Dayanidhi also likes Sarasu.
Savithri receives a letter from Seetha stating that her husband is handicapped and her plan to return to Chennai. Savithri is shocked and restless; she is not prepared to share her son with Seetha. Seetha and Munuswamy who had their own doubts about Savithri accepting them, are happy to see Savithri at the harbour but their happiness is short-lived. Instead of taking them home, Savithri takes them to her Tambaram guest house and categorically declares that Selvam is her son and they cannot come near him.
Savithri plans to get Selvam married to Rama (Leela), her relative's daughter, but Selvam refuses and declares he will only marry Sarasu, which upsets Savithri.
Munusamy falls sick and Seetha takes him to a hospital in a rickshaw. Selvam's car collides with their rickshaw and he treats them at a hospital and while dropping them home, he realises it's his parents' guest house at Tambaram. He tells them that he is Savithri's son. Munusamy and Seetha are happy to see their son, but do not reveal their identities.
Realising that it is hard to control their feelings for their son, Munusamy and Seetha leave the guest house and Savithri sends Dayanidhi to find them. He traces them and brings them back home. Noticing that Munusamy is ill, Selvam calls the family doctor home. Savithri is shocked to see Seetha and Munusamy in her house. Afraid that they will reveal the truth to Selvam, she forcibly takes Selvam to Rameshwaram. Munusamy calls out, follows them and falls down and dies. Savithri reaches Rameshwaram and gets a telegram about Munusamy's death. On their return, Selvam is shocked seeing Seetha as a widow. He feels guilty for leaving them suddenly, slips on the stairs and gets injured. Seetha comes to see him discreetly with the help of Sarasu. Noticing this, Savithri offers a blank cheque to Seetha and tells her to leave the house. Savithri also scolds Sarasu for betraying her. Seetha leaves the house and for being called a betrayer, Sarasu also leaves with her father.
Next day, Savithri gets a letter and since she uses reading glasses, asks Selvam to read it. When Selvam begins to read it, she realizes it's from Seetha and tries to stop him but her husband states it is time Selvam knows the truth. Reading the letter, Selvam raises doubts and Savithri's husband now reveals that Selvam is Seetha's son. Selvam shouts that Savithri has been harsh on his real parents and that she is not his real mother. Selvam goes in search of his mother, followed by Dayanidhi.
Selvam and Dayanidhi finally find Seetha and when Selvam falls at his mother's feet and asks for forgiveness, Seetha refuses to accept him and states that Savithri is his mother. But Selvam refuses, stating Seetha is his mother and he cannot leave her. Meanwhile Savithri falls sick and becomes almost insane as she is unable to live without Selvam. Savithri's husband rushes to meet Seetha and pleads with her to send Selvam back. Seetha says that if he agrees, she has no objection. Savithri's husband gets upset and tells her that Savithri is the real mother for Selvam, because Seetha could live without Selvam for 20 years but Savithri cannot live without Selvam for even 20 hours. Seetha realises her mistake and takes Selvam to Savithri. Selvam hesitates to address Savithri as 'mother', and Seetha slaps him. Savithri, who gains consciousness, asks her how she dares to slap her son. Selvam, realizes his mistake and understands Savithri's total love for him, and calls her as 'mother'. Savithri is happy, and says that he is not just her son; but also Seetha's. Selvam marries Sarasu and all of them live together happily.
[from the book Pride of Tamil Cinema: 1931 to 2013, G Dhananjayan, Blue Ocean Publishers, 2014]