Rajinikanth, Vijay Sethupathi, Simran, Trisha
Kaali is an elderly man who takes up a job as a boys hostel warden at a college in Darjeeling. When he first comes to the hostel, he notices it being dominated by a group of rowdy final-year students led by Michael, the son of a local leader, Gnanam. Kaali manages to put a full stop to Michael's antics, which leads to enmity between the two. Kaali forms a close bond with an NRI hostelite Anwar, who is in a romantic relationship with Anu, the daughter of a pranic healer, Mangalam. When Kaali meets Mangalam to convince her to accept her daughter's relationship with Anwar, they both fall 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, who ensures the suspension of he and his friends, with Anwar recording and sharing the humiliation of Michael and his gang. This video is noticed far away in Uttar Pradesh by a local goon Jithu, the son of a powerful politician Singaaram alias Singaar Singh. Singaar and Kaali have a past animosity and on seeing Kaali and Anwar in the video, he sends his men to Darjeeling to kill them both. 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, following which Anwar learns about his past.
Anwar is the son of Maalik, who was Kaali's best friend, with Kaali's real name being Petta Velan alias Petta. Twenty years ago, in a village in Madurai district, Maalik was in love with Poongodi, who was impregnated by him out of wedlock. When Petta heard of this, he and his wife Saro managed to convince Poongodi's father Rajapandi to get Poongodi married to Maalik, even though he and Petta were sworn enemies. But Rajapandi's two sons, Devaaram and Singaar, vehemently opposed the alliance as well as transfer of property to Poongodi and killed their father as a result. Petta, on hearing about Rajapandi's murder, killed Devaaram during Rajapandi's funeral and chased Singaar out of the village. In retribution, Singaar orchestrated a bomb blast during Poongodi's seemantham, killing Maalik, Saro and Petta and Saro's son Chinna. Petta found out that Poongodi was still alive and took her to safety. Poongodi gave birth to a boy, who was none other than Anwar, and both of them left for Australia as refugees to escape from Singaar. On hearing this story, Petta and Anwar, along with Michael, who has settled his differences with Petta, and his henchmen, leave for Uttar Pradesh to finish off Singaar.
In Uttar Pradesh, Petta and Anwar come into confrontation with Jithu, who is determined to kill them both after he also learnt about the animosity between Petta and his father. They manage to escape from him. Later, Petta meets Jithu privately and tells him that he is none other than his son Chinna, who did not die in the bomb blast, but was adopted by Singaar after finding out that he was still alive. When Jithu confronts Singaar regarding his parentage, the latter sends his men to kill Jithu, who is rescued by Petta. Along with Anwar and Michael's henchmen, Petta and Jithu then barge into Singaar's mansion and kill him and his henchmen.
Following Singaar's death, Petta has a surprise in store for Jithu. He reveals that Jithu is not his son and that he really is Singaar's son. He used him to lead him to Singaar as part of a strategy to kill the latter. He further adds that Chinna had died in the bomb blast twenty years ago and that the men he sent to kill Jithu were his own and not Singaar's. After this shocking revelation, the screen cuts to black and a gunshot is heard signifying that Petta killed Jithu.