Sivakasi alias Muthappa (Vijay) is a do-gooder in Chennai who works as a welder there. He enjoys life with his friends and forgets the past he left behind. He falls in love with a rich girl Hema (Asin) and her family accepts him as an honest and good man at heart. One day, he lashes out at his lover's brothers and Hema yells at him. Sivakasi gives her one slap and tells her that he was not the way he currently is. He tells her about his past.
Muthappa was a good boy who lived in a village named Nattarasan Kottai and who followed his parents orders. His elder brother Udayappa (Prakash Raj) who was a crook even as a child, tells him to get some fireworks for the village Deepavali festival. Muthappa obeys and Udayappa lights the firework. A woman stands on top of the bursting firecracker and begins to burn. She begs for life and is carted to the hospital. Their father (Rajesh) interrogates Sivakasi. Udayappa tells Muthappa to not tell that it was him. Muthappa is left in a long period of silence. Udayappa screams to the village that it was Muthappa. Their father thrashes Muthappa. Muthappa's sister and mother cry for him to stop, but their father pays no attention. Udayappa smirks and laughs throughout the thrashing. Muthappa is disowned and his father tells him never to show his face to him again. Muthappa secretly obtains several objects during the beating, his mother's bangles, the belt used by his father to thrash him, and his brother's glasses. Ashamed and no longer knowing who he is, Muthappa leaves for Chennai and changes his name and survives, with the sympathetic support of Venky and Mamoi, who together with Sivakasi, help him forget his past and start a welding business. Sivakasi soon makes a living as a successful welder and becomes the owner of the largest welding shop in the city, respected by the local people and a local hero. As a result, he slowly lets his horrific past drift away from him.