The film opens with former Chief Minister Naachiyar being sentenced to prison for his involvement in the Housing Board construction scam. Refusing to pay the penalty, Naachiyar vows to exact vengeance on the incumbent Chief Minister for putting him behind bars. Meanwhile, a notorious gangster Veera terrorizes the public, prompting the people to seek help from Annadurai “Dorai.” Dorai Arjun Sarja confronts Veera and his men, and in the ensuing clash Dorai kills Veera. ACP Eshwara Pandian Prakash Raj arrives at the scene, identifies Dorai as the killer, and begins to build a case, though he remains frustrated by the lack of evidence to arrest him. He warns Dorai that the law will catch up with him only when proof is found, and he chides Dorai for using violence as a shortcut to justice.
Dorai runs an orphanage called Annai Illam, a place that reflects his complex moral code. His violent reputation has driven a wedge between him and his own family, including his mother and his younger sister Susheela Sujatha. Susheela’s life, and the family’s finances, become precarious as Dorai’s actions ripple outward. A medical camp at the orphanage reveals a more urgent problem: contaminated water poisoning the children. Dorai confronts Rajaram, the owner of Zeo Leather factory, directly about polluting the source and endangering lives. Seizing the moment, he mobilizes the factory workers to strike and, in the process, pushes for the installation of a water processing unit in the plant—an act that heightens Rajaram’s fury and raises the stakes of Dorai’s vigilante approach.
Anjali, a TV reporter hosting a prank show, becomes drawn to Dorai after witnessing his commitment to public service. She devises a plan to get close to him by pretending to be an orphan and convincing the orphanage attender, Ayyanar Vadivelu, to let her stay at Annai Illam. Her wealthy father also moves in, keeping their real identities hidden. Together with the inmates, Anjali and Dorai are nudged toward a possible union, as she urges Dorai to marry her. Meanwhile, Dorai’s sister Susheela is betrothed to Prakash—an arrangement that complicates Dorai’s life—and the burden of wedding expenses falls on Dorai. Dorai secretly helps Susheela by assisting with Prakash’s promotion to manager at Zeo Leather, aided by Rajaram, who seems to have redirected his anger into reform. Three months pass, Naachiyar is released, and Dorai’s vigilante crusade continues as he kills a rapist and sends the body to the police, provoking ACP Eshwara Pandian to intensify his pursuit.
Anjali’s initial misjudgments about Dorai’s kindness lead to tension, but Subramaniam clarifies that the woman Dorai helped is Veera’s AIDS-stricken wife, and Dorai has been quietly supporting her. Subramaniam also unveils a flashback to Dorai’s past, shedding light on the roots of his harsh, justice-driven worldview. In flashback form, Dorai’s early life in Kumbakonam is shown: he works as a teacher and, during a paper-correction trip to Trichy, he rescues Subramaniam from a gang of goons and intervenes when a college instructor misbehaves with a student. This brave act costs him his job after he is brutally outspoken, angering his mother, who urges him to abandon violence as a path to righteousness.
Dorai’s backstory also reveals another layer of his history. Manickavel, another teacher, seeks Dorai’s help regarding substandard conditions at his school. Despite having reported the issues to the education department, Manickavel turns to Dorai due to inaction, and Dorai initially declines, heeding his mother’s caution to avoid taking the law into his own hands. Yet tragedy strikes when the school referenced by Manickavel burns down, claiming the lives of 48 children who perished due to insufficient escape routes. Dorai’s decision to confront the officials who allowed the neglect leads to his arrest and conviction for killing the District Education Officer, earning him a minimum three-year prison sentence.
In the present, Anjali learns more about Dorai’s past and recognizes the good in his heart, while Dorai accepts Anjali’s love. His mother, once a critic of his violence, grows to understand his motives and accepts him as well. Amid this personal reconciliation, Eshwarapandian plots to trap Dorai by feeding Naachiyar information about his activities. Naachiyar, hungry for revenge, engineers a bombing plot in Chennai. Dorai foils the plan by eliminating the terrorists and informing Naachiyar of his counter-move. In retaliation, Naachiyar poisons the orphanage’s food, killing Lakshmi and hospitalizing others. Dorai seeks vengeance, attacking Naachiyar’s farmhouse, only to be shot by Naachiyar and buried in a coffin.
Miraculously, Dorai escapes and recovers in a nearby clinic. When Naachiyar learns of his escape, he orders the police commissioner to execute an encounter killing. Eshwara Pandian, who has his own complex reasons for aiding Dorai, intercepts and orchestrates the kidnapping of five Human Rights Commission members to prove Dorai’s righteousness to the world, declaring that Dorai has done what the police could not—protect the public. He reveals his calculated involvement with Dorai in order to root out criminals and asks the commission to save Dorai from Naachiyar’s deadly plan.
On Vinayaka Chathurthi, Dorai quietly seeks a private conversation with Eshwara Pandian at a hospital, where the truth comes to light: Eshwara Pandian did assist Dorai in eradicating criminals. The inspector, mortally wounded, admits this last truth with his final breath, cementing Dorai’s status as a protector rather than merely a vigilante. With renewed resolve to stop Naachiyar, Dorai confronts his foe and discovers a bomb hidden inside a Ganesha statue that forms part of a procession capable of destroying thousands of lives. In a breathless finale, Dorai neutralizes the threat just as the procession reaches the beach, but Naachiyar wounds him fatally in the process. In the aftermath, Dorai—driven by his late mother’s guidance to stand up for the vulnerable and to act with courage—kills Naachiyar, offering a resolute, if tragic, end to a life defined by conflict between law, justice, and mercy.
