Balasubramanian alias Balu is an absent-minded but kind-hearted Tamil college Professor. He lives with his younger brother Raju, his maternal uncle Rangarajan and his cousin Sumathi, who is also his love interest. Raju, who studies in the same college that Balu works, is short-tempered, rowdyish and a drunkard, spoiled by Balu's and Sumathi's pamperings. He frequently gets into fights with a fellow student Raghupathy, whose father owns the college. Balu fails in several attempts to reform Raju. One night, Balu is accidentally killed when he tries to intervene in one of the fights between Raju and Raghupathy. Before dying, Balu asks Raju to ensure that he can find another person who can marry Sumathi as he does not want her to suffer after his death, to which Raju agrees with a heavy heart. Balu's demise marks a turning point for Raju, who vows never to get angry and drink again. Sumathi, who is devastated at Balu's death, goes into depression, dons the garb of a widow and vows never to marry. To ensure that Sumathi gets over Balu, Raju and Sumathi move to Bangalore, where Raju takes up a job at a garage owned by Devi.

One day, Raju encounters his brother's doppelgänger Shankar, a rowdy and thief who steals cars daily from the garage. Raju, who still feels guilty over his brother's death, is unable to fight Shankar as he looks like his brother and unsuccessfully tries to develop a bond with him. However, after hearing Raju's and Sumathi's sad story, Shankar undergoes a change of heart and he decides to mend his ways, eventually becoming a police informer. Soon, he falls in love with Sumathi, but Sumathi rebuffs him as she is unable to forget Balu. Meanwhile, Sumathi is kidnapped by a smuggler Bhaskar, for whom Shankar once used to work, in order to force him to smuggle diamonds. Shankar reluctantly agrees to Bhaskar's demand so that Sumathi would be saved, but when Bhaskar refuses to release Sumathi, a fight ensues between Shankar and Raju on one side and Bhaskar on the other side, which ends with Bhaskar's arrest. Sumathi realises her love for Shankar, and the movie ends with the marriages of both Shankar and Sumathi as well as Raju and Devi, with Shankar dressing up like the late Balu for the marriage.