Bhagyalakshmi, a young woman played by Sridevi, is in a car accident on her way home from a party and is hospitalized with severe head injuries. As she recovers, doctors diagnose retrograde amnesia, which leaves her unable to recognise her own parents and causes her to regress to a childlike state. While she undergoes treatment, she is kidnapped and sold to the madam of a brothel.
R. Srinivas 'Cheenu' [Kamal Haasan] arrives in Madras to meet his old friend, Y. G. Mahendran. The two visit the brothel for services, and the madam sends Bhagyalakshmi, renamed Vijaya, to Cheenu's room. Cheenu realises she is still a child and pities her, learning that she comes from a cultured family and was kidnapped into prostitution.
The next day, Cheenu returns and, after paying a huge sum to the madam, takes Vijaya out purportedly on a pleasure trip. He brings her to Ketti, where he works as a school teacher, and shelters her, tending to her as if she were a child. Viji, as she is called by Cheenu, forms a very close bond with him. When Viji accidentally spills ink on Cheenu's documents, anger flares up, threatening their fragile relation, but they eventually reconcile.
A local woodcutter named Natarajan [K. Natraj] lusts for Viji and nearly assaults her, but she manages to fend him off. Upon hearing the ordeal, Cheenu becomes enraged and nearly kills Natarajan, only to be restrained by neighbours who were alerted by Viji. Meanwhile, the wife of Cheenu's headmaster is attracted to him, though he does not return her feelings.
Viji's father Vedachalam [Veera Raghavan], who has been searching for his daughter through the police, places a newspaper advertisement about his missing child. A co-passenger who had travelled with Cheenu and Viji from Madras to Ooty provides a lead. Cheenu takes Viji to an Ayurvedic practitioner [J.V. Ramana Murthi] and leaves her there for a day of treatment. In his absence, the police come to his house in search of Viji, and the doctor confirms that Viji is receiving care at his clinic. The treatment eventually succeeds. Viji regains her memory, but she forgets the period between her accident and recovery. The doctor informs Vedachalam that the person who brought her there had been taking good care of their daughter; Vedachalam withdraws his police complaint, and the family begins their journey back to Madras with Viji.
After the police depart, Cheenu runs after the car carrying Viji, hoping to gain her attention at the railway station. She cannot recognise him. He performs like a dancing monkey—an old memory of a pastime she once enjoyed—but Viji, unable to comprehend, thinks he is insane and begs for food. Cheenu persists, but the train pulls away, and he, wounded from the chase and heartbreak, walks away.
