In 1986, Rayappan, a Tamil Nadu MLA from the ruling party, stands at a podium in J.K. Nagar, a destitute suburb of Chennai, where a laboring pregnant woman is swept into the scene as a publicity moment. To drum up sympathy, he orders his men to help the woman by lending their dhotis, and the newborn boy is christened Singaravelan, known on stage as "Singam." Singam grows up an orphan after his mother dies shortly after his birth and his father sinks into despair from heartbreak. The bond with his younger sister, Manimegalai, is tense and fractured; he blames her for their parents’ deaths, while she disapproves of his fixation on Rayappan, even recalling how he once sold their mother’s nosepiece for party promotions. The years pass without them speaking to each other.
Fast forward to 2021, [Rayappan] is a powerful, influential politician who starts scouting for a suitable councillor for J.K. Nagar. To catch his eye, Singaravelan performs a dramatic media stunt—drinking poison in front of the press during Rayappan’s arrest—and wins his trust, much to the irritation of Mangalam, Rayappan’s right-hand man who is also vying for the post. Singam’s rapid rise hinges on clever schemes and his ally Vasu’s ideas, helping him secure Rayappan’s favor. Frustrated by his sidelining, Mangalam lashes out and brandishes a bottle at Singam, leading to his expulsion from the party.
An eerie turn follows as Singam develops an alter ego that emerges after his injuries, doing the opposite of his public persona. The next day, Singam is nominated for the counsellor chair, but Rayappan requires a 50 lakh rupee deposit, which he has already acquired by duping Kamatchi, a wealthy moneylender’s daughter, with the help of Vasu’s goons. Kamatchi is later saved by Singam’s alter ego when the vigilante lashes out at the criminals. During the campaign, both Singam and Mangalam deploy corrupt tactics to woo voters. Singam initially trails in money and influence, so he leans into sympathy by carrying a pregnant woman named Shanti to gain public recognition, shocking Vasu, but he ultimately defeats Mangalam to become the new counsellor of J.K Nagar.
Then enter Damayanthi and the Mayor, who run an illegal construction and money-laundering scheme under the NGO guise of Aashirvaad Foundation. They approach Singam through Rayappan with a 50 crore bribe to evacuate and demolish J.K Nagar. Yet the vigilante alter ego resurfaces, leaking the contract to the media and painting Rayappan, Singam, and the ruling party in a corruption scandal. An outraged Rayappan calls an urgent party meeting, only to be confronted by the masked vigilante on CCTV. He orders Singam to locate the whereabouts of the money, and the reveal of the mask confirms the vigilante’s existence.
What follows is a tense cat-and-mouse chase as the vigilante exposes Singam’s corrupt plans, sowing distrust with Vasu who ultimately leaves him. When evidence mounts, Rayappan concludes that Singam is the masked enforcer, and he is abducted by henchmen before being caught by the income tax department during a money exchange. Bail comes from Kamatchi, who discovers the truth about Singam and breaks off the relationship in anger for exploiting her emotions. In a fit of rage, Rayappan orders Singam’s death in his own territory, but he is saved by Lakshmi (the woman Singam had used for political leverage) and the local community, though he collapses from his injuries.
In the hospital, Singam confronts the consequences of betraying the people’s trust. Inspired by Vasu and a final video from his alter ego exposing the money’s hideout, he reconciles with [Manimegalai], after he overpowers her exploitative boss who abused many women, even publicly shaming him. He gradually regains his reputation and becomes the people’s favorite MLA candidate by using the funds he had stashed away to fulfill his duties. Fearing defeat, a furious Rayappan abducts JK Nagar’s 40 children to squeeze out the remaining 40 crores, but the media reveals his atrocities and the CM, Nagaraja Chola, orders him sacked and arrested. In a final meeting with the CM, Singam proves his loyalty and ascends as JK Nagar’s MLA by navigating politics with a deft blend of integrity and ruthlessness, leaving [Vasu] surprised and acknowledging that the political world sometimes requires a balance of both good and evil to endure.
