Kayalvizhi Pandian, an upper-division clerk at the Valluvenpettai branch of the Madras Central Bank, is a vocal feminist and anti-Hindi imposition activist. She also writes stories under the male pseudonym Ka. Pandian, because female authors often face lower readership. In the village, she and her grandfather, Raghothaman "Raghu Thatha", previously shut down Bharathiya Bhasha Ekta Sabha, the Hindi organization led by Ranganathan, a feat celebrated by the villagers. Her parents push her toward marriage, which she resists. A promotion arrives with two conditions: a transfer to the Calcutta branch and passing the Hindi Pratmika exam.
Dr. Chandrasekar urges Raghu Thatha to undergo a barium swallow test for stomach pain. The test reveals stomach cancer, and Raghu Thatha begins treatment at the Madras Cancer Institute. Grief-stricken, he voices three final wishes: to savor biryani at Buhari Hotel in Madras, to take a photo with M. G. Ramachandran, and to see Kayal married. To fulfill this last wish, Kayal reluctantly agrees to marry, despite disliking the suitors her family presents. She proposes Selvan, Tamilselvan—the engineer seven years her senior who shares her progressive values and works on transmission towers for the people. But an anonymous letter reveals her true identity as Ka. Pandian, and Kayal grows wary of Selvan.
To avoid an arranged marriage, Kayal’s brother Shankar suggests she complete the Hindi exam and transfer to Calcutta. Kayal and her friend Alamelu set out to learn Hindi with Suneel, their bank peon. Selvan grows suspicious of Kayal’s secretive behavior and avoidance. She asks for an earlier exam date, which her manager, Ashish Gupta, arranges. Kayal and Shankar devise a plan: have someone impersonate her for the exam. Selvan trails Kayal to the exam center in Sitrur, far from Valluvanpettai. Kayal ends up smuggling out the question paper, which Suneel carries back to the village to answer. After many obstacles, the completed answer sheet reaches the exam hall just in time. Selvan confronts Kayal, but she speaks boldly and he leaves, seemingly defeated, hoping this will prompt him to call off the marriage.
Yet Selvan learns from his mother that Kayal has seen his diary, where he expresses anger and a view of her plan to stop the wedding. He meets Kayal and pretends to reform, accepting whatever decision she makes, thus foiling her plan again. Meanwhile, Ranganathan has been trying to reopen the Valluvanpettai Hindi Sabha for two years, seeking revenge for the humiliation he suffered at Kayal’s hands; he finally gains permission and also receives an anonymous letter from Selvan revealing that Kayal took the Hindi exam for a promotion and that her marriage plans are underway.
As the wedding preparations progress, Kayal’s sister-in-law Poonkothai suggests abducting the groom. An anonymous letter, supposedly from "Suman," lures the groom to an isolated place, where he is beaten and locked up. Kayal breathes relief that the marriage seems halted, but Selvan unexpectedly reappears, and the proceedings resume. Ranganathan crashes the wedding to announce the reopening of the Hindi Sabha, prompting Kayal to interrupt the ceremony and vow to stop him. She reveals that she took the Hindi exam solely to prevent her marriage. When Selvan claims ignorance about the reason for stopping the wedding and asks for an explanation, Kayal accuses him of impotence, hoping to provoke his true male chauvinistic nature. Selvan’s anger surfaces, and the truth about his attitude becomes clear. The doctor later discloses that Raghu Thatha’s stomach issues were misdiagnosed as cancer, prompting Raghu Thatha to slap the doctor for the prolonged confusion. Despite his earlier pretenses, Selvan still tries to project reform, but his mother sees through the act and slaps him, ending the engagement.
Later, as Kayal sits at a bus stop, an ardent reader named Kamal, inspired by Ka. Pandian’s feminist and progressive stories, expresses a desire to meet the author. Kayal then reveals herself as Ka. Pandian, stepping out from behind the pen name at last.
