Pudhupettai is about Dhanush, who is a poor slum boy runs away from his home after his father, a small time rowdy, kills his mother. He leads a fairly humdrum life on the streets begging for a living until a chance meeting with a gang that sells narcotics. Kumar's life is never the same again. The gang is ruled by Anbu and his is a totalitarian system where people who oppose him are eliminated without trace. A local politician (Azhagam Perumal) supports his clandestine activities. Dhanush feels attracted to Sneha, a prostitute who works for Anbu. A fight ensues between them and Dhanush kills Anbu and becomes the leader of the gang. The remaining part of the movie tells how Dhanush establishes himself as a ground-breaking criminal and a henchman for a political party.