Plot

Kaaliyan has a sister who marries a young man without the permission from Kaaliyan and moves to Kolkata with her husband , where she faces unknown threats. Soon her brother Kaaliyan comes to the rescue.

Kaalaiyan (Rajinikanth) is a village president who only bows to goodness and moral fairness. These ideals lead him to clash with Nattadurai (Prakash Raj), a rival village leader who chooses to rule by fear. The 2 come face to face in a town police station over a dispute over land records. Kaalaiyan beats up Nattadurai's men in front of him.

When Nattadurai tries to extort land from an old man, he hires Pattamal (Nayanthara), a lawyer, to defend his case. Kaalaiyan exposes the truth to her (That Nattadurai had only paid for part of the land and was now trying to swindle the whole land, without paying for it. That part of the land is where the old man's wife is buried and hence he is fighting for it), leading Pattamal to intentionally throw the case, After a few days, Pattammal and Kaalaiyaan fall in love. At a temple in a neighboring village, Nattadurai tries to attack Kaalaiyaan with some of his men, but they all get thrashed. Nattadurai joins the fight himself, but has a change of heart when Kaalaiyan refuses to attack him in front of Nattadurai's family (wife (Sriranjini)).

Kalaiyan's world revolves around his sister, Thanga Meenatchi (Keerthy Suresh), whom he had to raise himself after their parents died (Mother died in child birth of the sister, while dad died earlier). When she returns home after completing her education in the north, some members of their family feel that it's time to get Meenatchi married, and they convey the same to Kaalaiyaan. Unsure of the suggestion, he consults with his sister about the idea, and she tells him that it's his decision that matters the most to her.

Kaalaiyan initially has trouble finding a suitable groom. All the grooms are afraid of Kaalaiyan. At the same time Kaalaiyan's Cousin Sisters, Angayarkanni (Khushbu) (Idithangi (Pandiarajan), Angayarkanni's husband) and Mangaiyarkarasi (Meena) (Irulandi (Livingston), Mangayarkarasi's husband) wants to marry their brothers (Sathyaseelan (Sathish), Angayarkanni's brother, Mangayarkarasi's brother (Sathyan)) to marry Thanga Meenakshi. They both initially wanted to marry Kaalaiyan 10 yrs ago, But he didn't accept to marry them, as they were blood relations. Now the cousins want Kaalaiyan to decide which sister's brother he wants to marry Meenakshi to.. When Kaalaiyan is unsure, the cousin sisters offer to divorce their respective husbands and marry Kaalaiyan.

After a lot of drama and understanding, they allow Thanga Meenakshi to marry anyone of Kaalaiyan's choice (after he pulls a godly chariot with hooks dug into his back, as penance for a better life for his sister). Finally he agrees to let Meenatchi marry Nattadurai's younger brother who is a doctor in a Govt hospital. The day of the wedding, Meenatchi goes missing, so Kaalaiyan dispatches men to search the entire countryside. They finally find Meenatchi on a train, trying to elope with a boy she met during her studies. Torn between his need to save his family's dignity and his love for his sister, Kaalaiyan finally allows Meenatchi to leave.

An understanding Nattadurai peacefully leaves, and Kaalaiyan staves off demands for an honor killing from relatives (Kaalaiyaan's grandmother (Kulappulli Leela), Kaalaiyan's uncle (Vela Ramamoorthy), Kaalaiyan's uncle (Piraisoodan)). Meenatchi shifts to Kolkata with her husband, where she loses contact with Kaalaiyan. Worrying about her well-being, Kaalaiyan and Pattamal travel to Kolkata to find her. Kaalaiyan accidentally eavesdrops on Meenatchi, when he finds out that she is having serious troubles and can't bring herself to contact her brother unless she is happy and financially secure.

Kaalaiyan secretly follows Meenatchi to a bar where she meets a gangster who loaned her money to tell him that she can't pay him yet. When the gangster tries to assault her, Kaalaiyan grows enraged and beats up the man and his men. He does not reveal himself to Meenatchi and keeps his presence a secret. Kaalaiyan has Meenatchi moved to Pattamal's apartment, where he can watch over her while he tries to fix her problems. Meenatchi is threatened by thugs watching her through the window and falls ill. When Pattamal leaves to get her medicine, the thugs attack her. Kaalaiyan rescues her and interrogates the attackers, learning the truth of what happened to Meenatchi.

When she and her husband started business in Kolkata, they were approached by Manoj Parekar (Abhimanyu Singh), a wealthy businessman and underworld boss. Manoj tells them that he has forced many companies to let him purchase half of their shares to change his black money to white money, and that he wants to do the same to Meenatchi's company. Meenatchi's husband refuses, but Manoj warns Meenatchi that she will soon be pleading at his feet to sign over the shares. Over the following weeks, Meenatchi's company is destroyed: their factory catches fire, they are forced to shut down, and Meenatchi's husband is arrested under trumped-up charges, being tortured in police custody. Meenatchi falls at Manoj's feet and pleads him to get her husband released, signing over her company. Manoj agrees, but immediately backs down from his promise, saying that Meenatchi's husband will never be free again. Meenatchi tries to free him through legal means, but Manoj has everyone who agreed to help them murdered.

Hearing this story, Kaalaiyan swears to destroy Manoj Parekar. Going by the name Annaatthe, Kaalaiyan and some of his village friends storm Manoj's office and issue him an ultimatum: by the end of the week, Manoj will be dead. Manoj tries to find Annaatthe, but in vain. Annaatthe makes Manoj's life hell as he attacks him relentlessly, sets his business on fire, sets his personal Beemer on fire (with Manoj in it).. Manoj lands in the hospital.

Annaatthe tells Manoj and his gang members that unless they kill each other, Annaatthe will kill them himself. After escaping from his former subordinates, Manoj is cornered by Kaalaiyan, who forces him to sign his name on papers which says that he will return the companies he stole to their former owners. Kaalaiyan decides to spare Manoj's life, saying that death would be a mercy for him. Insulted, Manoj visits his estranged brother, Udhav Parekar (Jagapathi Babu), demanding that Udhav end "Annaatthe". After saying this, Manoj suicides. Udhav manages to track down Meenatchi (he sends men to all families who had their money returned to them. But Kaalaiyan saw the men coming and thrashed them. This was the only group who didn't report back to Udhav and that's how he tracks them down) and brings men to attack her, realizing that Annatthe would surely arrive to protect her. Pattamal and Meenatchi manage to evade the attackers for some time (with Kaalaiyan guiding Pattamal on phone from a high vantage point from where he surveys all proceedings), but are separated by a crowd. Kaalaiyaan arrives and clobbers all of Udhav's men and kills Udhav. He reveals himself to Meenatchi, who tearfully apologizes for all the trouble she put her brother through.