Parimalam, a school drop-out, is a mischievous and nubile girl who perennially plays pranks on unsuspecting people in her village, aided by her gang of preteen boys. These pranks often end her and the gang in the panchayat, which is headed by her father. An unnamed man with an infant child is appointed as the new teacher of the village's only school. When he comes to the village with his infant for the job, he is not spared from Parimala's pranks upon his arrival. The teacher takes classes by holding the book in one hand and rocking the cradle with the other in the classroom, much to the amusement of the villagers who call him "Vaathiyar".

Parimalam's playful nature transforms into love when she learns that Vaathiyar is a widower. She tries many ways to win his love, but fails every time. Vaathiyar believes that a stepmother would not take proper care of his child from his first wife, and even rejects a proposal to marry his deceased wife's sister. The deceased wife's last words – that he should take care of the child well after she dies – keep echoing in his ears often. Parimalam visits Vaathiyar and openly requests him to marry her, but he rejects her and throws her out. Deciding to marry him by any means possible, she lies to her father and the villagers that Vaathiyar had sex with her, knowing that the panchayat would order him to marry her to preserve her chastity.

A public trial is held, during which Parimalam is questioned if Vaathiyar had had sex with her. She commits perjury, and Vaathiyar is forced to marry her. In revenge, he stipulates that Parimalam has to remain a virgin for life as punishment for cheating him. He does not treat her as his wife. However, Parimalam is persistent and does everything possible to come closer to him. She relentlessly tries to seduce him by unconventional methods that prove to be testing times for Vaathiyar.

Vaathiyar's former mother-in-law gives him a metal trunk box, belonging to her late daughter. Not knowing its contents, he sends it home to Parimalam. When Parimalam opens the box, she finds jewels and costly sarees owned by Vaathiyar's late wife. She dons the jewellery and goes to brag about it to her village friends. Meanwhile, Vaathiyar's son swallows a coin while playing with a neighbour, and Parimalam gets the child to take home. The child becomes sick, and is saved by the village doctor at the last minute. Angered that Parimalam's carelessness almost killed his son, Vaathiyar banishes Parimalam, and she is taken to her father's home.

Weeks later, Vaathiyar discovers the truth regarding the coin incident, and feels sorry for Parimalam. When Vaathiyar fights with some people who are not supplying mid-day meals adequately to the schoolchildren and is almost stabbed, she saves his life by holding the edge of the knife. She suffers deep cuts on her hands and Vaathiyar takes her back and nurses her to recovery. He also tries to take out Parimalam, but once they leave, the photo of his deceased wife falls and breaks due to wind. Vaathiyar takes this as a bad omen and stops the plan. He also saves one of his students, who was about to be killed by his stepmother. He fears such treatment for his son in future.

Parimalam understands why Vaathiyar is hesitating to consummate the marriage; he fears she would ignore and mistreat his son when she has a child of her own. She decides to undergo sterilisation to gain his confidence and gets admitted into a hospital. By then, Vaathiyar learns of this and rushes to the hospital to stop it as he now understands her good intentions and does not want her to suffer. He reaches the hospital to find Parimalam unconscious on the bed and assumes she has already undergone treatment. However, the doctor assures him that she has not been operated as he found her to be a virgin and realised that she must have wanted the operation under duress. The couple unite and consummate their marriage.