Thami movie tells the story of Angry young man Thambi Velu Thondaiman (Madhavan) who fights against all types of evils in the society. So, he runs into Sankara Pandian (Biju Menon) who is a local rowdy who is a terror to the locals. He decides to reform him.
Archana (Pooja) who is a student of the college sees Thambi fighting with gangsters,and mistakes him to be a goon. However, she changes her heart after hearing Thambi's troubled life in the past.
Thambi's past life, in particular how his entire family is killed by Annachi's gang. She falls in love with him later after realizing his true nature. How Thambi manage Shankara Pandian is told in reviting climax.