In Kolkata, Kathir is a prisoner who helps the police trap an escaping detainee, Vivek Banerjee, but ends up slipping away again after the capture. In Chennai, he plans to flee to Bangkok with his friend Ravi, a plan that shifts the moment he falls in love with Ankitha. Later, Kathir and Ravi witness thugs shooting Jeevanandham 'Jeeva', a man who bears a striking resemblance to Kathir. They admit him to a hospital, and Kathir decides to impersonate Jeeva to outsmart the police.
Under the guise of Jeeva, Kathir and Ravi enter a retirement home run by Jeeva, intending to steal ₹25 lakh (roughly US$47,000 in 2023) to fund their Bangkok trip, until Kathir uncovers Jeeva's broader mission. Jeeva was a communist ideologue and hydrology postgraduate from the arid village of Thanoothu, in Tirunelveli district, who had uncovered groundwater beneath local lands that could sustain irrigation for the region. A greedy entrepreneur named Shirag swindled villagers into ceding their lands for a factory, leading to Jeeva's arrest and provoking six villagers to take their grievances to the media in hopes of Jeeva's release.
Moved by Jeeva's past, Kathir takes up the villagers' cause while still posing as Jeeva. The people in the retirement home, along with Kathir, go to the jury to press their case, but Kathir begins to introduce his own rules and unsettles the main juror bribed by Shirag. He even arranges a ruse by sending a person disguised as a hairdresser to Shirag, prompting Shirag to have a fingerprint placed on his own neck. In response, Shirag sends fifty men to kill Kathir, yet he fends them off with resourcefulness and grit.
Meanwhile, Jeeva finds himself in the Kolkata prison. With the help of Vivek, who has heard Jeeva's story and plans to kill Kathir, he escapes along with Vivek’s henchmen. Unaware that Jeeva is en route to Chennai with those mercenaries, Kathir press gangs the media into national attention to spotlight the villagers’ plight.
A few days later, at the Madras High Court, the judge rules in favor of Jeeva and the villagers but adds a caveat: Shirag claims that several villagers abroad have expressed support for the factory. If they cannot prove Shirag faked that support within five days, the verdict will swing in Shirag’s favor. With the overseas supporters unreachable on short notice, Kathir takes drastic measures to keep the issue alive, coordinating a dramatic water blockade in Chennai by sitting on the pipelines—joined by Ankitha, Ravi, and the retirement home inmates—so the city feels the impact.
News of the nationwide outcry amplifies Kathir’s cause. He reappears and frames the villagers’ plight for the media, ensuring the story remains in the public eye. Kathir learns that Jeeva has escaped and is heading to Chennai with Vivek’s henchmen. Shirag’s men kidnap Jeeva, and the sight of Kathir’s televised speech moves Shirag, who begins to grasp the depth of his own misdeeds. On the eve of the verdict, a phone call exposes Kathir’s bluff, but he pledges to help the villagers and tells them that Jeeva is alive and will rescue him.
Kathir goes to Shirag’s office, rescues Jeeva, and kills Shirag. The next day, the judge declares the verdict in favor of Jeeva and the villagers. Despite the victory, Kathir does not join the celebrations; instead, he surrenders to the police after promising Ankitha that he will marry her once he is released.
