Ezhil, is a civil engineer from IIT Madras, while his lookalike Kavin, is a gambling thief who deceives people along with his sidekick Suruli. Ezhil's love interest is an IT girl Deepika, while a girl named Ananthi, loves Kavin, unaware of his real identity. One day, Kavin tries to help Suruli pay his debt by extracting money from Ananthi through lies, but she helps him in spite of knowing the truth. After taking the money, Kavin is enraged, and so is Ezhil after a party. That night, one of them breaks into a house and attacks the owner Akash, stabbing him to death. The next day, Kavin frees Suruli by paying his debt and wins Ananthi's trust by returning her money and telling her the truth. However, as the investigation of Akash's murder proceeds, a selfie clicked by a couple nearby is found with either of Ezhil or Kavin in it.

Both Ezhil and Kavin are brought in and investigated without their knowledge of each other's existence. Gopalakrishnan, inspector who shares an old rivalry with Ezhil, tortures him. Ezhil reveals his car broke down, and a call taxi driver helped him, as he didn't have the repair kit. SI Malarvizhi interrogates Kavin, who on the other hand, cites various laws to escape torture. She reaches out to Akash's friend and shows him the photograph of Ezhil/Kavin, but he refuses to recognize him. She also questions Suruli and tells him not to leave the city without permission, but he secretly escapes. Malarvizhi then learns of the rivalry between Ezhil and Gopalakrishnan; Ezhil helped the latter's daughter elope with her lover, much against her father's wishes. The forensic expert informs Malarvizhi about a hair sample recovered from the crime scene and how it doesn't match anyone else in Akash's home.

At the police station, Ezhil tries to escape but is interrupted by Kavin. The two violently fight, hurting everyone and vandalizing the station in the process. Kavin and Ezhil are revealed to be identical twins after their DNA is found identical, and both confess about the same; they parted ways when their parents divorced. Kavin went with his mother, who used to gamble a lot, but wouldn't refuse anyone who asks her help, and one day tried to convince him that she'd give up gambling, but instead committed suicide. Kavin was then taken in by his father but got into a violent fight with him and Ezhil. Both of them were admitted into a mental institution as a result. Growing up as their father died, Kavin became interested in studying the law but left studies due to his lack of college ethics. One day, when Kavin came home and left in front of Ezhil, whose ring for Deepika went missing, Ezhil reported him to the police.

The police beat up Kavin, who himself told Ezhil to look for the ring in the drawer. Ezhil realized his mistake, but Kavin, who came home for a photo of their mother, vowed to seek revenge. On the other hand, Gopalakrishnan still wants to frame Ezhil, but the call taxi driver who helped Ezhil confirms he was really stuck on the night of the murder. It also gets proved that Kavin paid Suruli's debt with gambling money he won after playing all night. The sessions court, weeks later, acquits both Kavin and Ezhil in order to protect the innocent one from punishment. Gopalakrishnan retires without getting his revenge. Months later, while shifting the items of the Police station, Malarvizhi gets glimpse of Deepika's photo in Akash's case, and calls Akash's friend to inquire about the girl he was infatuated with, and was shocked to learn that it was Deepika. Ezhil is finally revealed to have murdered Akash for drugging, kidnapping and raping Deepika to death out of his childhood lust. Akash also bribed the police to avoid charges. When Kavin found out about Akash's murder, he helped Ezhil by getting officially arrested himself as well to throw off the police.

Later, Kavin meets Ezhil on the highway and explains how Malarvizhi can't reopen the case as she created a fake witness to help Ezhil, and could herself get arrested, having done this once which resulted in her suspension. Ezhil hands him over a photograph of them with their mother and tells him he is going to Mumbai, and later to Copenhagen, never to return. Having sold all of his property in India, Ezhil gives a 50% share to Kavin as a tribute. After his marriage with Ananthi, Kavin realizes his lack of trust in his mother prompted her to kill herself. He promises to do better with his wife.

Seven months later, some of the investigating officers appear for a documentary shooting. One of the investigating officers calls the case unprecedented, before someone tells him similar cases occurred in other countries as well.