Pandian, Kamal Haasan, an assistant dance choreographer with a modest income, lives in a small, tight-knit home with his wife Janaki Meena and their daughter Bharathi Baby Anne. After five years of marriage, Janaki grows increasingly unhappy with the cramped life and Pandian’s limited time for the family, and she applies for a divorce. Her wealthy father Vishwanathan Iyer, Gemini Ganesan, supports the move, and Janaki gains sole custody of Bharathi, leaving Pandian with only a weekly chance to see his daughter. Bharathi loves her father deeply and dislikes the idea of their separation, sensing that something in the household has changed.
Basha, Nassar, Pandian’s longtime friend, pushes him to win Bharathi back by taking her away from Janaki. Pandian reluctantly agrees, but the plan backfires once he is discovered, and he loses even the chance to meet Bharathi for a while. The tension between duty, love, and disobedience deepens as Pandian clings to the hope of a family, while the reality of the divorce grows heavier.
In a bid to stay close to Bharathi and to rescue his fractured family, Pandian learns that Vishwanathan has advertised for a woman to look after his granddaughter. In a conversation with Joseph, a makeup artist, Nagesh cooks up a bold plan: Pandian will transform himself into an elderly, dignified Iyer woman named Avvai Shanmugi, so he can be present in the house without arousing suspicion. Avvai Shanmugi, Kamal Haasan, makes his entrance as a job applicant, but is initially rejected because another nanny has been chosen. Yet fate has other plans.
When Bharathi is hurt while fireworks are going off, Shanmugi responds with a quick, practical rescue that involves pulling Bharathi into a swimming pool to cool the burns, a decision that surprises the household and even the family doctor, who praises the unconventional but effective treatment. Vishwanathan is impressed enough to drop the earlier hire and invite Shanmugi to stay. Before long, the whole family—Janaki and Bharathi in particular—begins to warm to Shanmugi’s presence, finding comfort in her calm demeanor and practical wisdom. Bharathi, during her moments with Shanmugi, begins to see a familiar spark and recognizes that Shanmugi has a deep connection to her father, though she chooses to guard the truth.
Rathna, a girl who loves Pandian, becomes another thread in the growing fabric of misunderstandings. Basha, now posing as a mute Iyer cook, earns admission to Vishwanathan’s household on Shanmugi’s suggestion after the previous cook is caught stealing. The ruse nearly unravels when Vishwanathan’s secretary Sethuram Iyer catches Basha mid-prayer, exposing the disguise and triggering a cascade of comic and tense moments. Yet Shanmugi’s sincerity slowly wins over the household; Vishwanathan grows fond of her and even contemplates proposing, while Mudaliyar, the house owner where Pandian lives, also finds himself drawn to her.
Meanwhile, Pandian begins to sense that Janaki has not entirely forgotten him. Shanmugi subtly rebuffs Vishwanathan’s advances by insisting that her husband is alive, while Pandian tells Sethuram Iyer that Mudaliyar is Shanmugi’s husband. The web of pretenses thickens until Shanmugi convinces Vishwanathan that Janaki’s rightful place is beside her husband. As Vishwanathan steps aside to discuss family matters with his estranged son-in-law, Shanmugi finally reveals her true self to Basha by removing her blouse, a moment that Janaki witnesses and misreads as a seduction.
A desperate Janaki speeds to Pandian’s house to reclaim what she thinks is hers, but the sight of Rathna waiting and Shanmugi’s clothes scattered around leads her to fear that her husband may be unfaithful. She drives to a bridge and attempts suicide, only for Shanmugi to intervene, saving her and revealing the identity beneath the disguise as Pandian. The truth reassembles the family: Janaki and Pandian reconcile, while Pandian, in a final, bittersweet gesture, “kills off” Shanmugi by attributing her apparent drowning to the rescue of Janaki. The family is united, and the drama of disguises, love, and loyalty comes to a poignant close, with the bond between husband and wife stronger than before.
