Thambi Velu Thondaiman (Madhavan) is a rebellious youth who cannot tolerate violence and injustice by any means. His main target is Sankara Pandian (Biju Menon), a rich local goon. Thambi wants Sankara Pandian to leave all his illegal activities and violence. One day Thambi interrupts Archana's (Pooja) stage performance when chasing a wrongdoer. Archana misunderstands Thambi as a rowdy and hates him, but Thambi saves Archana in a restaurant when a few guys try molesting her, following which she starts liking him, which gradually transforms into love. However, Thambi does not reciprocate and wants Archana to stop following him as he has so many enemies in the city.
Thambi is invited to his alma mater to preside for a function where he opens up his personal story. A flashback is shown where Thambi was leading a joyful life with his parents and sister. Once, Thambi spots a murder committed by Saravana Pandian (Shanmugarajan), Sankara Pandian's brother. Thambi becomes the murder witness and identifies the murderer in court, which angers Sankara Pandian. To avenge his brother's arrest, Sankara Pandian murders Thambi's parents and sister. This made Thambi transform into a fearless youth trying to make the city free from violence.
Thambi wants Sankara Pandian to transform into a good guy and prevents all his plans to erupt violence in the city. Finally, Sankara Pandian brings in violence and clashes in the city one day for political reasons. Unfortunately, his mother suddenly suffers a from heart attack, and he rushes to the hospital with her. On the way, however, his car gets blocked in traffic as there is violence everywhere on the roads, and he could not reach the hospital on time. Thambi comes to the spot, and Sankara Pandian thinks that Thambi will take revenge on him by killing his family. However, to his surprise, Thambi lifts Sankara Pandian's mother from the car and runs to the hospital. Sankara Pandian's mother is saved, following which Sankara Pandian realizes his mistake and admires Thambi's great affection for the well-being of every person although not related to him. He also decides to leave all his violence and illegal activities and apologizes to Thambi for his wrongful acts committed. In the end, Thambi and Archana unite.