Bhagyalakshmi (Sridevi) has a car accident while returning from a party and is hospitalised with severe head injuries. When she recovers, she is diagnosed with retrograde amnesia and she fails to recognise her own parents. She mentally regresses to the state of a child. While she is undergoing treatment, she is kidnapped and sold to the madam (Ganthimathi) of a brothel. Srinivas, also known as Cheenu, (Kamal Haasan) comes to Chennai to meet his old friend (Y. G. Mahendra). Together, they visit the brothel to relax. The madam sends Bhagyalakshmi, renamed Vijaya, to his room. Cheenu realises that she is mentally still a child and pities her. He learns that she is from a cultured family, and that she was kidnapped and forced into prostitution.
He returns the next day and, after paying a huge sum to the madam, takes Vijaya out, supposedly on a pleasure trip. He takes her away to Ketti, where he is working as a school teacher. He takes her to his residence, where he protects her and also pampers her like a child. Viji, as she is called by Cheenu, has completely forgotten her past and becomes very close to him. When Viji accidentally spills ink over Cheenu's documents, angering him, their relationship is threatened, but they reconcile. Later, a local woodcutter named Nataraj (Nataraj) lusts for Viji and nearly assaults her, but she manages to save herself. When she tells Cheenu about it, he becomes livid with rage and almost kills Nataraj, but is stopped by his neighbours who were informed of the incident by Viji. Meanwhile, the wife (Silk Smitha) of Cheenu's boss is attracted to Cheenu, though he does not reciprocate her feelings.
Viji's father Vedachalam (S. R. Veeraraghavan), who was searching her through the police, releases a newspaper advertisement about his lost daughter. A co-passenger who had travelled with Cheenu and Viji from Chennai to Ooty by train gives them a lead. Cheenu takes Viji to an Ayurvedic medical practitioner (Ramanamurthy) and leaves her there for treatment for a day. In his absence, the police come to his house searching for Viji. Finally, the police learn that Viji is getting treated at the doctor's place and reach there. Cheenu is unable to come as he is afraid of police action. The treatment goes through successfully. Viji regains her memory and completely forgets about the period between her accident and recovery. Vedachalam and his wife are happy and decide to leave. From the doctor, Vedachalam learns that the person who had brought her there had been taking good care of their daughter; he withdraws his police complaint and they begin their journey to Chennai with Viji.
After the police leave, Cheenu comes running after the car in which Viji is travelling. He follows them to the railway station and tries to gain the attention of Viji, but she is unable to recognise him. Cheenu acts like a dancing monkey that Viji developed a liking for, but Viji, unable to comprehend, thinks that he is insane and begging for food. Cheenu continues his futile attempts to gain her attention, and the train eventually leaves with Viji not recognising him. Cheenu, who was hurt while chasing her car and trying to get her attention, is left alone, heartbroken.