Aachaarya movie is a poignant story of young man (Vignesh) who takes to crime to earn a living and later treat a transformation path after realizing his past mistakes. Yadhunandhan (Vignesh) who is an unchavriti Brahmin boy is an orphan. He leaves his village near Madurai to earn his living. He comes across Mayakka (Vadivukkarasi) who is a vegetable seller in market. Mayakka, a tough female is leader of own a rowdy gang. she takes him under her wings.
Yadhu becomes Samy and he befriends the rival group leader Annavi Thevar (Nasser) and other goons in the market. In a brutal gang war, Mayakka is killed by the rival group. Samy and his friends are on the run to escape police. But he is after Thevar to revenge Myakka's death.
How Samy, with the help of his girlfriend Divya and the local cop, Thiruvachagam IPS (Charanraj), fights to bring Thevar to justice is narrated in the remaining part of the movie.