Ezhil, Arun Vijay a civil engineer from IIT Madras, leads a quiet life until his lookalike, Kavin, Arun Vijay enters the scene as a gambling thief who schemes with his loyal sidekick Suruli, Yogi Babu. While Ezhil longs for a stable future, Deepika, Tanya Hope — an IT professional — becomes his love interest, and a young woman named Ananthi, Smruthi Venkat, secretly loves Kavin, unaware of his true identity. The web of deceit begins when Kavin attempts to help Suruli repay a debt by pulling a fast one on Ananthi, only to have her respond with unexpected kindness despite harboring the truth.
After taking the money, a storm erupts: Kavin is furious, and so is Ezhil after a party they attend ends badly. That night, one of them breaks into a house and murders the owner, Akash, Yesakkiappan, stabbing him to death. The following day, Kavin frees Suruli by settling his debt and wins Ananthi’s trust by returning the money and speaking the truth. As the murder investigation progresses, the police uncover a selfie taken by a nearby couple that seems to include either Ezhil or Kavin.
Both men are summoned for questioning, unaware of each other’s existence. Inspector Gopalakrishnan, Fefsi Vijayan, who has an old rivalry with Ezhil, tortures him. The interrogations also involve Malarvizhi, Vidhya Pradeep, who grills Kavin and cites various legal measures to avoid harm. She tracks down Akash’s friend and shows him the photo, but he cannot recognize the suspects. She also questions Suruli and orders him not to leave the city, though he secretly escapes. As the case unfolds, Malarvizhi learns about the rivalry between Ezhil and Gopalakrishnan; it’s revealed that Ezhil once helped the latter’s daughter elope against her father’s wishes. A forensic expert reports a hair sample from the crime scene that does not match anyone else in Akash’s home.
At the police station, Ezhil tries to escape, but Kavin interrupts, and a violent clash erupts, with both men wreaking havoc in the station. DNA tests reveal that Ezhil and Kavin are identical twins who confess to the same crimes. Their backstory unfolds: the brothers split after their parents divorced, with Kavin going with their mother, who gambled compulsively and eventually died by suicide. Their father raises Kavin but gets into a brutal confrontation with him and Ezhil, culminating in their admission to a mental institution. Kavin had once shown an interest in law but abandoned it due to a lack of college ethics. In a tense moment, Kavin helps Ezhil by getting into trouble and getting arrested to mislead the authorities, even as Ezhil tries to reconcile with his past.
The narrative shifts as the case continues to hinge on framing attempts by Gopalakrishnan; a taxi driver who aided him confirms he was stuck on the night of the murder and had paid Suruli’s gambling debt with his own money. A sessions court eventually acquits both Kavin and Ezhil to protect the innocent. Meanwhile, Malarvizhi uncovers Deepika’s photo in Akash’s file and questions Akash’s friend about the woman he was drawn to. In a dramatic flashback, it’s revealed that Ezhil murdered Akash for drugging, kidnapping, and raping Deepika, acting on childhood lust, and bribed the police to drop the case. Kavin aids Ezhil by courting danger and even choosing to be arrested to throw off the authorities.
On the highway, Ezhil hands Kavin a photo of the two of them with their mother and reveals plans to leave for Mumbai, then Copenhagen, never to return. With India sold, Ezhil allocates half of his stake to Kavin as a parting tribute. After his marriage to Ananthi, Kavin confronts the truth about his mother’s death and resolves to be a better partner for his wife. Seven months later, documentary teams arrive to recount the case; an investigating officer calls it unprecedented, only to hear that similar patterns have appeared in other countries.
