Durai Singam (Suriya) is the honest police sub-inspector of Nallur, a small village in Thoothukudi district in southern Tamil Nadu, assisted by his bumbling colleague Erimalai (Vivek). He belongs to Nallur with his father, Soundarapandi (Radha Ravi) having a respectable status in the village. His family business is provision stores and Durai Singam wants to join it, but he joined police due to Soundarapandi’s wishes. He resolves most of the problems in his village with non-violence and mutual counselling. He uses force only when the situation demands it, thereby gaining much reputation and love from the villagers. Mahalingam (Nassar), an industrialist in Chennai and a friend of Soundarapandi, comes to the village with his daughters Kavya (Anushka Shetty) and Divya. Durai Singam initially mistakens Kavya as a thief, when she is about to prank her cousin by wearing a tiger costume and roam around the village, accidentally slaps her. As Kavya is about to take revenge on Durai Singam, he apologizes to her, Kavya got moved by this, slowly fell in love with him. After some hilarious incidents, Kavya proposes to Durai Singam. Initially taken aback, soon Durai Singam reciprocates Kavya’s love.
Chennai-based Mayil Vaaganam (Prakash Raj), a big-time extortionist with shady mafia dealings who blackmails people by complaining to the Income Tax Department, is required to travel to Nallur to sign a conditional bail. He instead, sends one of his allies to do the formalities, much to the anger and rage of Durai Singam who demands Mayil Vaaganam sign the bail in person. Humiliated, Mayil Vaaganam reaches Nallur but is unable to take any revenge on Durai Singam fearing the immense love and devotion of the entire village towards Durai Singam. Using his political contacts, he gets Durai Singam transferred to Chennai to teach him a lesson.
Durai Singam, unaware of Mayil Vaaganam’s hand behind his transfer, joins Thiruvanmiyur police station. His co-worker, Sub-Inspector Ravi (Bose Venkat), hates Mayilvaaganam for his crimes but is unable to take any action because of Mayil Vaaganam’s political powers. The Assistant Commissioner of Police, Rajendran (Nizhalgal Ravi), Durai Singam’s senior, is on Mayil’s payroll and takes care in concealing and eliminating the evidence of Mayil Vaaganam’s crimes from the eyes of the law. The Police Commissioner (Ajay Rathnam) also does not help Durai Singam as there is no evidence against Mayil Vaaganam and Rajendran and in turn, warns him to stay away from Mayil Vaaganam’s case.[clarification needed] Unable to take on Mayil Vaaganam in his stronghold, Durai Singam wants to return to his village, but is stopped by Kavya who encourages him to fight against the evil and not run like a coward.
Being mentally tortured by Mayil Vaaganam, Durai Singam arrests Mayil Vaaganam’s brother Vaikundam (Adithya Menon) in a fake case of illegally smuggling alcohol. He thwarts off Rajendran in full view of the public when Rajendran, bounded by his duties to Mayil Vaaganam, tries to protect the henchman. Meanwhile, Mayil Vaaganam kidnaps Kavya’s younger sister for ransom. Rescuing her, with unexpected help from the Home Minister, Ramanathan (Vijayakumar). Durai Singam successfully traces the origins of the kidnapping racket to Mayil Vaaganam. Durai Singam also gets promoted to Assistant Commissioner of the specially-formed Anti-Kidnapping Task Force. Mahalingam, who was hostile to Durai Singam following an altercation with Soundarapandi back at Nallur, softens up and agrees to give him Kavya’s hand in marriage.
The entire police force , including the Police Commissioner, and Rajendran, now on Duraisingam’s side, decide to help Durai Singam fight Mayil Vaaganam. They manage to kill Mayil Vaaganam’s henchman in an encounter at a hospital and begins to target everyone and everything related to Mayil Vaaganam. In retribution, Mayil Vaaganam starts targeting everyone close to Durai Singam, including Kavya, whom he shoots but is saved by Durai Singam, and Ravi, who is hacked to death by Mayil Vaaganam’s henchmen. To escape the arrest warrant issued out to him, Mayil Vaaganam kidnaps the Karnataka Home Minister’s daughter. He falsely tells Durai Singam that he is going to Pondicherry with her when actually he is going to Nellore in Andhra Pradesh to put the police off the track. However Durai Singam manages to pursue them till Gudur near Nellore, where he rescues the home minister’s daughter and kills Mayil Vaaganam in an encounter. After that, he resigns his job publicly in a felicitation function organised for him.
During the credits, Durai Singam is seen with Kavya heading back to Nallur, and as when Durai Singam is stopped briefly by Ramanathan who offers an undercover mission, to which Durai Singam willingly agrees.