Raghu, Dhanush lives with his family in Pollachi. His older brother Thiru, M. Sasikumar, left their house after his girlfriend was killed during a biking trip. Raghu is in his final year of computer science and engineering when he meets an actress named Lekha, Megha Akash; she is forced to act against her will. After a few encounters, they become friends and the relationship grows into love. Raghu brings Lekha home to introduce her to his parents, and they warmly welcome her. Yet troublesoon follows when a film director named Kuberan and a producer arrive at Raghu's house and take Lekha away after threatening Raghu's family. Raghu is left heartbroken, believing Lekha has dumped him.
Four years later, Raghu receives a call from Lekha, who tells him she is with Thiru and that he is in trouble, urging him to come to Mumbai. Raghu travels there and discovers that Thiru is actually an undercover police officer trying to expose an illegal arms deal and is now on the run as the police close in. Thiru is arrested and taken to court, where the police and goons attack him. Raghu arrives, answering Thiru's call, and with Thiru's senior Arun Bhide they subdue the attackers; Thiru escapes without Raghu being seen.
Lekha had earlier asked Raghu to come to a location where he finds her held at knifepoint. He rescues Lekha and they escape in an auto, where Thiru suddenly appears and the brothers briefly reconcile. The auto is attacked, and Thiru is killed in the ensuing shootout, leaving Raghu devastated.
Before the fateful confrontation, Thiru had given Raghu a keychain and told him to keep it safe. Lekha then reveals what happened after Kuberan abducted her: he wanted Lekha to act in more films against her will and had tortured his own son and wife to coerce her, forcing her to act out of fear for Raghu and his family. Kuberan takes her to Mumbai, where he pimps her to other actors, but Thiru rescues her. Thiru later asks Lekha to join him and Raghu hides her at his college senior Mythili's room to keep her safe.
Kuberan learns Lekha's location and arrives with DCP Nagaraj to take Lekha away. Raghu fights Kuberan, and in the struggle he stabs Nagaraj (the man believed to be behind Thiru's death), then escapes again with Mythili and Lekha, determined to clear his brother's name. Raghu visits the gym Thiru had frequented but finds the locker empty. Police arrive with DCP Suraj and arrest Raghu. Meanwhile, Kuberan returns with Lekha and Mythili, and Raghu is taken to Thiru's safe house, where he attacks the police officers before being shot by Nagaraj. One of the officers shoots Nagaraj, and the room is sealed.
Saved by the keychain, Raghu discovers a hidden table with a keyhole that fits the key Thiru gave him. Behind it lies a hard disk and a laptop that reveal the illegal arms dealings carried out by several influential people, including Kuberan. Raghu calls Kuberan to arrange a meeting to hand over the hard disk. The police arrive, and Raghu shoots them dead. Thiru's name is finally cleared, and those involved are arrested. Raghu arrives at his sister's wedding with Lekha and Mythili, and after secretly performing Thiru's last rites, tells his parents that Thiru is safe and working as a police officer. In a closing voice-over, Raghu vows to hunt down everyone responsible for Thiru's death.
