Arjun Ramakrishnan (Vishal) comes to Chennai to woo a psychology student named Divya (Tamannaah), on whom he has a crush. With the help of a local incompetent don named Deva (Soori), he succeeds in winning her heart. Divya's elder brother is Tamizhselvan (Jagapathi Babu), the honest and sincere DCP of Chennai. He approves of the relationship between Arjun and his sister, and soon, their wedding is fixed. One day, Tamizhselvan is kidnapped by some goons in retaliation for his thwarting of a black money scam six months ago. Arjun rescues Tamizhselvan and takes him home, only to reveal that he is a CBI officer who had discovered ₹250 crores stashed in Tamizhselvan's house as black money. ₹300 crores had been seized during the black money raid, but it was publicly announced that only ₹50 crores had been seized. Arjun takes away all the money but does not arrest Tamizhselvan due to his public reputation, instead of telling him to personally surrender later that day.

However, Tamizhselvan soon finds out that Arjun is not a CBI officer, but is a criminal who had recently been released from prison. He pursues Arjun to get back the money. During the chase, he opens fire on Arjun's SUV, causing Arjun to lose control and meet with an accident, losing consciousness. Arjun wakes up in a hospital, having lost his memory. Tamizhselvan keeps Arjun in custody in a house, where a psychiatrist named Dr. Boothri (Vadivelu) is assigned to restore Arjun's memory so that he can reveal where he has kept the money. Unknown to anyone, Arjun had not lost his memory; he is only pretending as part of his mission to retrieve the black money. At night, he sneaks out of the house and steals the black money of a Union Minister (Jayaprakash), converting it to white money with the help of a hawala trader. However, Tamizhselvan and the Union Minister soon find out that Arjun had not lost his memory and had stolen even more of the black money. Arjun, confronted by Tamizhselvan and the Union Minister, reveals his motive for stealing the black money.

Arjun is from Manimangalam, a remote village with no basic amenities like roads, water, high schools, and even proper housing and sanitation facilities. When the building of the only primary school in the village collapsed, he confronted the local MLA Sivagnanam (Thennavan), who had falsely claimed to have developed the village, by pocketing all the money which was to be used for developing Manimangalam. Sivagnanam rudely sent him away, defending his corruption and even declaring that he would never develop the village. Following this, Arjun approached the Union Minister, who also turned out to be corrupt like Sivagnanam. Arjun's friends confront Sivagnanam and his men, who kill them all, including Sivagnanam. It is at this stage that Arjun had decided to get back all the black money acquired by Sivagnanam (which was the ₹300 crores recovered earlier in the film) and the Union Minister and use it to develop Manimangalam.

Arjun takes Tamizhselvan, the Union Minister, and Divya to Manimangalam, which is now a very well-developed village. He reveals that he had used the money hoarded by the Union Minister along with Sivagnanam's ₹300 crores to develop the village and had given the credit to him, because of which the villagers now hold the Union Minister in high regard. Tamizhselvan drops all charges against Arjun, seeing that he had stolen the money which was black for good intentions, and arrests the Union Minister. In the credits, it is revealed that Divya and Tamizhselvan involve themselves in Manimangalam's development, along with Arjun.