Kaali is a mysterious and deceivingly elderly man, who takes up the job of a boys' hostel warden at a college in Ooty. He notices that the hostel is dominated by a group of unruly final-year students, who are led by Michael, the spoiled son of a local leader named Gnanam. Kaali puts a stop to Michael's antics, which leads to enmity between the two. Kaali also forms a close bond with a NRI hostelite named Anwar, who is in a relationship with Anu, the daughter of Mangalam, a pranic healer.

Kaali convinces Mangalam to accept her daughter's relationship with Anwar, and they end up falling in love. Michael, who lusts for Anu, is angered on hearing of her relationship with Anwar, and attempts to harass them, only to be stopped by Kaali. Michael and his friends are suspended, where Anwar records and shares the humiliation of Michael and his gang. The video is noticed in Uttar Pradesh by a local goon named Jithu, the son of a powerful politician called Singaaram aka Singaar Singh. Singaar, on seeing Anwar in the video as well as in a photo with his mother on Facebook, sends his men to Ooty to kill Anwar, for unknown reasons.

At the same time, Michael, humiliated at his suspension, sends his men to beat up (but not kill) Kaali. Michael's plan backfires as he and his men are caught in the fight between Kaali and Singaar's men. Kaali subdues Singaar's men, earning Michael's and Gnanam's respect, following which Anwar meets Kaali's friend, who narrates about his past. Anwar is the son of Maalik, who was Kaali's best friend. It is also revealed that Kaali's real name is Petta Velan, who is a well-respected man in his village in Madurai.

Past: Maalik learns that Devaram and Singaar were involved in illegal sand mafia, which leads to Devaram getting arrest by Maalik and Petta. Petta learns that Maalik was in love with Devaram and Singaar's sister Poongodi, who conceived with him out of wedlock. Though relucant, Petta finally agrees, where he and his wife Saraswathy "Saro" managed to convince Poongodi's father Rajapandi to get Poongodi married to Maalik, but Devaaram and Singaar vehemently opposed the alliance as well as the transfer of property to Poongodi. After Maalik and Poongodi's marriage, Devaram and Singaar kill Rajapandi.

On hearing about Rajapandi's murder, Petta kills Devaaram during Rajapandi's funeral and chased Singaar out of the village. Enraged about Devaaram's death and his forced exile, Singaar orchestrates a bomb blast during Poongodi's seemantham, killing Maalik, Saro and Petta's son Chinna. After finding that Poongodi is still alive, Petta took her to safety. Poongodi later gave birth to a boy, who is revealed to be Anwar and both of them left for Australia as refugees to escape from Singaar.

Present: On learning his past, Anwar, along with Petta and Michael's henchmen leave for Uttar Pradesh to finish off Singaar once and for all. Petta and Anwar confront Jithu, who is determined to kill them both after learning about them from his father. The duo manages to escape Jithu. Later, Petta meets Jithu privately and reveals to him that he is none other than his son Chinna, who did not die in the blast, but was adopted by Singaar after finding him still alive in the wreckage. When Jithu confronts Singaar regarding his parentage, the latter sends his men to kill him, who is rescued by Petta.

Along with Anwar and Michael's henchmen, Petta and Jithu barge into Singaar's mansion where they kill him and his henchmen. Following Singaar's death, Petta reveals that Jithu is not his son and that he really is Singaar's son. Petta used him to lead to Singaar as part of a strategy to kill the latter. He further adds that Chinna had died in the bomb blast. After this shocking revelation, Petta helds Jithu at gunpoint and kills him.