Kaalaiyan is a stereo typical sarpanch in Soorakkottai, Thanjavur who bows to moral fairness but don't know about feminism. These ideals lead him to clash with a rival village leader Nattadurai, who rules by fear. When Nattadurai tries to extort land from an old man, he hires Pattammal, a lawyer, to defend his case. Kaalaiyan exposes the truth and Pattammal withdrew the case. Pattammal and Kaalaiyaan soon fall in love.

Kalaiyan's world revolves around his sister, Thanga Meenatchi, whom he has lovingly raised after the death of their parents. After she returns home having completed her education, Kaalaiyan faces difficulty in finding a groom for her as everyone is afraid of him. Kaalaiyan's annoying cousin sisters, Angayarkanni and Mangaiyarkarasi, both propose that their brothers marry Thanga Meenakshi. They had both wanted to marry Kaalaiyan but he had not agreed. A lot of drama follows. Thanga Meenakshi's marriage is arranged with Nattadurai's younger brother.

The day of the wedding, Meenatchi escapes from his superstitious brother. Kaalaiyan dispatches a search party who catch Meenatchi on a train, trying to elope with her boyfriend from college. Torn by his love for his sister, Kaalaiyan allows Meenatchi to leave and staves off demands for an honour killing from relatives. Meenatchi shifts to Kolkata with her husband and loses contact with Kaalaiyan. Kaalaiyan and Pattamal travel to Kolkata. Kaalaiyan finds out that his sister has serious financial troubles. He secretly follows her and finds out she idiotically has borrowed money from a gangster.

When the gangster tries to assault Meenatichi, Kaalaiyan secretly beats him up and moves Meenatchi to Pattammal's apartment, where he can watch her getting beat. Meenatchi is threatened by thugs watching her and falls ill. When Pattammal leaves the house to get her medicine, the thugs attack her. Kaalaiyan rescues her and interrogates the attackers, and learns the truth.

When Meenatchi and her husband started a business in Kolkata, they were approached by Manoj Parekar, a wealthy businessman and underworld boss. Manoj wanted to purchase half of their shares but Meenatchi's husband had refused. Over the following weeks, Meenatchi's factory had caught fire, they were forced to shut it down, and her husband was arrested under trumped-up charges and was being tortured in police custody. Meenatchi had begged Manoj to get her husband released and signed over her company. Manoj had refused to get him released and got everyone who agreed to help her murdered.

In the present, Meenatchi is still trying to get her husband released with Pattammal's help, only to realise that she is pregnant. Kaalaiyan is very happy on hearing this and he and Pattammal organise a baby shower for her.

After learning the truth behind Meenatchi's misfortune, Kaalaiyan wanted to kill gangsters by using his sister as a bait and swears to destroy Manoj Parekar. Under the name of Annaatthe, Kaalaiyan and his village friends storm Manoj's office and issues an ultimatum. After more drama, Annaatthe corners Manoj and forces him to sign his name on papers saying that he will return the companies he stole to their former owners. Kaalaiyan decides to spare Manoj's life.

Humiliated, Manoj visits his estranged brother, Udhav Parekar, demanding Annaatthe be finished and then commits suicide. Udhav tracks down Meenatchi and brings men to attack her. Pattammal, instructed by Kaalaiyan, hides her. Pattammal and Meenatchi are chased by the men until the two are separated by a crashing auto-rickshaw. Kaalaiyaan arrives and clobbers all of Udhav's men and kills Udhav. He finally reveals himself to Meenatchi, who tearfully apologises for all the trouble she put her brother through.