The film opens with the voice of Basheer, a veteran prison guard with thirty years of service, who narrates how a riot at Madras Central Prison triggers a formal inquiry led by the Tamil Nadu minister and his appointed panel. The commission, headed by retired Ismail, begins digging into the events that sparked the violence and the deeper forces at work inside the facility. At the center of the tale is Kattabomman, a long-time prison employee who sets the stage by recounting the rise of Siga, a notorious gangster who still exerts control over both the prison and the surrounding city through his wealth and influence. Accompanying Siga is his trusted, volatile associate, Tiger Mani, whose bursts of anger underline the perilous dynamic inside the walls. Also unusual in this setting is Kendrick, a reformed former juvenile drug dealer who has embraced spirituality and now preaches the teachings of Jesus, earning the affection of his fellow inmates. On a nudge from Kendrick and with Seelan's advice, Siga and his circle abandon their old ways, convert to Christianity, and Siga eventually undergoes baptism.
Into this fragile equilibrium steps Parthi, a new inmate who is falsely accused of murdering former IAS officer Shanmugam. Ismail, sensing a miscarriage of justice, begins to investigate Parthi’s life and his fiancée, Revathy, who helps shed light on Parthi’s world. Parthi, who runs a roadside eatery with his mother, is romantically involved with Revathy, the owner of a nearby flower shop. The case appears crooked from the start: Shanmugam was a regular customer who had offered a loan, and a police inspector with a grudge against Parthi uses circumstantial evidence to frame him for murder. When the inspector humiliates Parthi’s mother, Parthi fights back, and the violence snowballs, leading to his arrest and the further insinuation of Siga’s involvement.
Inside the prison, Parthi starts asking about Siga and his world, drawing the ire of Siga’s associates. A brutal assault on Parthi by Mani intensifies the stakes, but Siga intervenes to stop the attack, underscoring the hold he still maintains in the facility. Around this time, Kattabomman learns that a deserved promotion to jail superintendent has been withheld in favor of Sunil, a cunning reform-minded officer installed to curb Siga’s influence. When Mani is caught drug peddling, Siga is publicly humiliated during a frisking episode that strips him of dignity, and the power struggle within the prison deepens.
Sunil, aiming to use Parthi against Siga, assigns Parthi to work in the prison kitchen under [Bashir Bhai], while Parthi befriends Mohan and Rangu in a bid to gain allies. Parthi discovers Rangu being sexually exploited for VIP prisoners, and Sunil harshly confiscates Kendrick’s Bible and beats him, driving Kendrick into a fearful state that ends in tragedy. Kendrick’s death spurs Siga to lash out violently at a police officer, but Seelan cautions the gang that Sunil’s inhumane treatment must be exposed to the public—especially on Christmas Day when a reporter and church sisters visit the prison.
In the days leading up to Christmas, Sunil quietly releases Parthi, using him as a pawn in a plan to force Siga’s hand. He engineers a meeting between Parthi and his mother and manipulates Parthi into thinking that if Siga admits he did not hire Parthi to kill Shanmugam, Parthi will walk free. A scheme repeats: Sunil feeds a laxative-laced dish to Siga, hoping it’s poison. Parthi believes the powder is poison is misguided, but Mani, unaware of the deception, feeds the adulterated food to Siga. Before consuming it, Siga tells Parthi that he had no involvement in Shanmugam’s murder. Transported by Sunil to a prison hospital in Vellore, Siga dies en route when the adulterated meal, compounded by a second toxin, takes its toll.
The news of Siga’s death ignites a violent uprising across the prison as inmates seize control, attack the guards, and break free from their cells. Mani asserts himself as the new power broker, while Siga’s rivals vow to eliminate him. Seelan and Mani plot to leverage the chaos to force the government to take action, including the arrest of Sunil and the release of inmates awaiting investigation. Sunil, however, resists, and the situation spirals into intensified clashes. Parthi seeks to rescue three captive MLAs, a solo mission that sets the stage for a wider confrontation between the inmates and the authorities. Meanwhile, Mohan warns Mani that Parthi possesses a powder causing digestive problems in some inmates, and Mani, suspecting Parthi of involvement in Siga’s death, orders his men to find and kill him.
As the truth begins to surface, Parthi reveals to Sunil via walkie-talkie that he did not poison Siga. Sunil promises Parthi release in exchange for information about the three MLAs, and a hot confrontation erupts with a gunfight inside the prison. Bashir Bhai is fatally shot, and in his dying moments he accuses Parthi of betrayal. A fierce duel between Mani and Parthi ensues, but other inmates intervene, and Sunil finally confronts Mani. Kattabomman informs Ismail that, upon entering the prison after an hour, he found most inmates dead. It later emerges that Kattabomman and his team killed the inmates who were negotiating peace, and that he had supplied Siga with the poisoned halwa through Mohan, then shot Siga himself. The inmates confront Sunil about Bashir’s death, and when Sunil begins to reveal the truth behind Siga’s poisoning, Parthi kills him to silence the confession.
In the aftermath, Kattabomman and Parthi publicly accuse [Mani] of killing Sunil, while Parthi privately argues with Ismail that, just as Shanmugam’s murderers remain unknown, so too will Sunil’s killers. Ismail closes the case with lingering doubt, noting that one of the MLAs jailed during the riot has become Home Minister and ordered the probe. Parthi’s family rebuilds their small eatery into a thriving restaurant, and Kattabomman earns a promotion to Superintendent of the prison. Ismail remains convinced of Parthi’s innocence but puzzled by Parthi’s willingness to shoulder responsibility for everything that happened inside the prison. The two men, Kattabomman and Parthi, share a quiet, knowing glance that hints at shared secrets.
The film ends with Parthi, now a powerful, almost kingpin-like figure within the prison, gazing at his engagement photograph. Ismail reflects on the warning in Kattabomman’s words: “There are only two paths in life: either kneel down in Heaven or be the King in Hell.”
