The underworld don Billa (Ajith Kumar), featured on Interpol’s criminal list, is hiding and operating out of Malaysia. DSP Jayaprakash (Prabhu) has spent the last few years looking for Billa, leaving behind a life in India.
During a chase with the police, Billa is severely wounded after an accident and dies in front of the DSP. The DSP then secretly holds a burial of Billa. Interpol officer Gokulnath (Rahman) is assigned to work with DSP Jayaprakash to capture elusive Billa as no-one knows of Billa’s death. DSP Jayaprakash keeps the death of Billa as a secret even from his fellow officers, and tracks down a look-alike called Saravana Velu (Ajith Kumar), a lowly pick-pocket. He asks Velu to infiltrate Billa’s gang by pretending to be Billa. In return he will make sure that the child Velu adopted, Karan, gets a proper education.
The DSP trains Velu and sends him back to Billa’s gang as a person who has lost his memory. Slowly Velu starts to learn about Billa’s gang and even speaks to Jagdish, Billa’s boss, on the phone. Velu provides a pen drive with the secret information of the crime network to the DSP, but he is about to be killed by Sasha (Nayantara) because her brother Rajesh as well as his fiancée Rhea (Hazel Keech) were killed by Billa. At this juncture, the DSP arrives and tells her that he is Velu and not Billa. Later before a party, Velu secretly provides information to the DSP about a meeting of Billa’s network and C.J. (Namitha), Billa’s girlfriend, overhears his conversation. She challenges Velu but in the fight, he accidentally kills her. A shootout occurs at the party and the DSP is secretly killed by Jagdish, leaving his gun behind. Velu finds the DSP’s body and the gun, but is taken into the custody of the police team, now headed by Interpol Officer Gokulnath. He argues during interrogation that he is Velu and not Billa to Gokulnath. Velu mentions a piece of evidence – the pen drive which may prove his innocence but the pen drive is nowhere to be found.
Unable to prove his innocence, he escapes from a police van. He phones Gokulnath and ask him to meet at the Aero bridge. Here it is revealed that Gokulnath is none other than the Underworld Crime Don Jagdish (Rahman) and he is the one who killed Jayprakash. Officer Anil Menon apparently had the pen drive all along and strikes a deal with Velu to get hold of Jagdish. Meanwhile, Sasha and Karan have been kidnapped by Jagdish and wants the pen drive in return for it. Velu meets Ranjith and gives him a second pen drive with the same data, but corrupted. Sasha is tied up with her mouth gagged with a strip of tape along with the boy. When Ranjith tries to kill Velu, a scuffle ensues making Ranjith fall from the top. In a final confrontation, Jagdish fights with Velu. Jagdish posing as Gokulnath asks the police to arrest Velu as Billa but gets shot by the squad of police and dies as the police have wired the entire conversation between Jagdish and Velu, thus proving his innocence. Velu finally hands over the original pen drive to Officer Menon as the film ends.