Set against the backdrop of a village near Kodaikanal, Vettai Naai revolves around Sekar (RK Suresh), a small-time rowdy, who seeks redemption post his marriage.

Maruthu (Vishal) is a labourer from Rajapalayam who personally does not tolerate injustice anywhere. He leads a happy life with his grandmother Appathaa (Kulappulli Leela) and his younger brother Kokkarako (Soori). One day, he encounters Bhagyalakshmi alias Bhagyam (Sri Divya), a bold young woman, at a temple, but their first meeting does not go well due to a misunderstanding, and he ends up at a police station. However, with Appathaa’s help, Maruthu soon manages to win Bhagyam’s heart. One day, he sees some goons chasing Bhagyam and her father (G. Marimuthu) near the market where he is working. Maruthu beats up the goons and then learns from Bhagyam’s father why the goons are after them.