Kamal Haasan, Meena Durairaj, Gemini Ganesan
The film starts in a courtroom where Janaki (Meena) is fighting for divorce from Pandian (Kamal Haasan). She offers various reasons for wanting a divorce. She has married Pandian against the wishes of her rich father Vishwanathan Iyer (Gemini Ganesan). But she isn't able to come to terms with living in Pandian's small house without amenities. Pandian is an assistant dance director with a modest income and is not able to spend much time with the family. All this accumulates and Janaki decides to apply for divorce, which is granted. The court orders that Pandian can meet his daughter Barathi, once a week and this is his only solace. His daughter, however, loves him a lot and doesn't like the arrangement.
Basha (Nassar), a friend who works in a hotel as a chef, advises Pandian to steal his daughter from Janaki. Pandian goes about trying to do as his friend suggests. In doing so, he is discovered; and now he cannot meet her at all. Then Pandian finds out that Vishwanathan Iyer has advertised for a woman to look after his granddaughter. Joseph (Nagesh) is a makeup man in films. In conversation with him, Pandian gets the idea of playing an old woman, so that he can be with his child and ex-wife without them knowing. Joseph agrees to this plan and the transformation is done from Pandian to 'Avvai Shanmugi' a dignified, elderly woman who is hired to take care of the little girl.
Rathna (Heera Rajgopal) is a girl who is in love with Pandian but is constantly rebuffed. Basha takes up the role of a mute Iyer cook and is admitted into Vishwanathan Iyer house on the recommendation of Avvai Shanmugi. However, Basha is caught later while doing his namaz, thereby shattering both lies that he is mute and an Iyer. Hilarious circumstances follow and slowly Avvai Shanmugi manages to convince the household of "her" sincerity. So much so that Janaki's widowed father begins to develop a liking for Avvai and in fact proposes to "her" too! Around the same time, Mudaliyar (Manivannan), the house-owner of the place where Pandian lives, happens to bump into Avvai Shanmugi. This happens many times and Mudaliyar, too, begins to develop a liking for "her".
Meanwhile Pandian slowly begins to realize that Janaki hasn't totally forgotten him. Avvai rebuffs Vishwanathan's proposals by saying that 'her' husband is alive. Adding to the chaos, "she" tells Vishwanathan that Joseph is 'her' husband; while Pandian tells Sethurama (Delhi Ganesh) Vishwanathan's secretary - that Mudaliyar is Avvai's husband. There is much confusion after this, but it is resolved at last. Avvai Shanmugi convinces Vishwanathan that Janaki's right place is by her husband. While Janaki's father goes off to talk to his estranged son-in-law, Avvai Shanmugi reveals 'her' true self as Pandian to Basha. This is seen by Janaki, who misunderstands the scene and believes Avvai to be an immoral woman. Janaki goes to Pandian's house to reclaim him, but upon seeing Rathna waiting there, and Avvai's clothes lying around, thinks that her husband, too, is promiscuous. Janaki leaves and attempts suicide, but Avvai Shanmugi stops her. Avvai reveals "her" identity as Pandian. Janaki and Pandian reconcile.