Kali (Rajinikanth), a hard-working winch operator at a powerhouse, brings up his sister Valli (Shobha) and is more than a brother to her. He flouts official rules by permitting the villagers to travel on the winch, for which he gets reprimanded by the new Divisional Engineer Kumaran (Sarath Babu). Kali starts disliking Kumaran for halting his helping activities. When Manga (Fatafat Jayalakshmi) and her mother reach the village with no assets and no one to assist them, kindhearted Valli helps them set up home in their village. Manga is very playful and often teases Kali; once she teases Kali when he is on duty. He abandons the winch and chases her. In his absence, an emergency crops up at the powerhouse, and an angry Kumaran suspends Kali temporarily for the negligence of duty.
Very upset at his suspension, Kali gets drunk and swoons on the road. In a freak accident, a lorry runs over his hand, which is amputated. Because of this handicap, he loses his job. Though depressed, he is confident of recovering from the situation. Manga feels guilty as she is the root cause of the crisis and happily agrees to marry him when Valli proposes it.
Kumaran likes Valli but hesitates to express it. After Kali is terminated from work, Kumaran approaches Kali for permission to marry his sister. Though Kumaran is good looking, educated, and well employed, Kali spurns the proposal because he hates Kumaran. He then makes arrangements to get Valli married to a loafer Kumarasamy (Venniradai Murthy). Knowing that Valli too likes Kumaran, Manga requests Kali to get Valli married to Kumaran, but he stubbornly refuses. Hence she decides to conduct the wedding without his concurrence, convinces Valli and Kumaran for this, and makes all arrangements.
On the day Kumarasamy is to wed Valli at his house, Kali learns that everyone has left to attend Valli's marriage to Kumaran. He intercepts the group of Valli and other guests walking towards the venue and reminds Valli about his love and how difficult it would be for him to live without her. Everyone else ignores him and moves on, Valli runs towards him, hugs him, and assures him that she would not disown him at any cost. A proud Kali turns towards the villagers, Kumaran and Manga, and asks how can they face him now and perform the wedding? Then, in an unexpected twist, he proudly offers his sister's hand to Kumaran. Though he hates Kumaran, he manfully accepts his sister's choice.
[from the book Pride of Tamil Cinema: 1931 to 2013 by G Dhananjayan, Blue Ocean Publishers, 2014]