Sethupathy (Kamal Hassan) is an honest and upright police officer. When he arrests four corrupt but powerful men, Dharmaraj (Nagesh), Francis Anbarasu (Delhi Ganesh), Nallasivam (Nasser) and Satyamoorthy (Jaishankar), they escape justice easily and return to take revenge.
They kill him and poison his wife (Srividya). She escapes and gives birth to twins with the help of another woman Muniyamma (Manorama), but the babies are separated and each woman believes that the other is dead because of the events that took place right after the birth.
One of the twins, Raja (Kamal Hassan) grows up as a mechanic with Muniyamma, while the other twin, Appu (Kamal Haasan), a dwarf, grows up in the circus with his mother. Appu falls in love, but when he is rejected summarily, and unable to bear the pain of not being considered due to his height, he tries to commit suicide.
However, he is prevented by his mother, who then reveals that his dwarfism might have been because of the poison force-fed to her when she was pregnant with the twins. This leads Appu to learn about his father’s murder and he decides to avenge by killing the four murderers.
The crux of the story follows how Appu carries out his revenge, and how Raja is mistakenly blamed for his crimes. Will Appu succeed in avenging his father's murder? Will their family ever reunite?