Gautham is a schizophrenic Indian rock musician who is missing 25 percent of his grey matter. He as a hallucination that a mysterious person he believes is one of the three murderers of his parents. As a child, Gautham was convinced that he was an orphan and assumes that his parents are dead; he does not remember their names or what they looked like.
At one of his concerts, Gautham sees one of the three men and chases him. Sameera, a journalist at the concert, films Gautham fighting his imaginary opponent. Gautham surrenders to the police after 'killing' the man, confessing that he killed three men: one in Belfast, one in Pune and one just now in Hyderabad. He is released from custody after Sameera broadcasts the video on television.
According to his doctor, if Gautham can hallucinate a person other than the three men, he can be treated. Gautham goes to Goa on vacation. Sameera stalks him, convincing him that two people are stalking him: a journalist who wants to interview him (imaginary), and a person claiming to be his fan (real). Gautham begins to fall in love with Sameera. He saves her from a group of people trying to murder her; on an isolated island together Gautham learns the truth behind the fourth imaginary person and writes Sameera off as a disturbed journalist. By the time he learns about Sameera's intentions, she has left for Hyderabad; Gautham pursues her.
In Hyderabad, Gautham accidentally spoils Sameera's birthday plans, infuriating her. Although he is convinced that he has made up an enemy to cope with being an orphan, a mysterious person tries to kill Sameera. Gautham saves her and proposes marriage, which she accepts.
Sameera learns that the mysterious person is Antonio Rosarios, a Goa-based crime boss who wants to kill her because she tried to expose the presence of hydrogen cyanide in seeds sold by Rosarios' company, AG1. Gautham meets Rosarios in the lobby of Sameera's office building. Assuming that he is an illusion, he shoots Rosarios in his head.
By the time Gautham realises Rosarios is real he is dead, and Gautham learns that his parents were murdered. He catches an aged taxi driver who was stalking him (one of the three men he imagined), and learns that two London-based Indians (one of whom was Rosarios) killed his parents; his father gave the taxi driver a bag to give to Gautham. In the bag is an old Rubik's Cube, a key and a British coin.
Gautham and Sameera go to London, where they and their driver Gulaab Singh escape from a murder attempt; Gautham's manager, Michael, is killed. The Rubik's Cube, when solved a certain way, reveals a safe-deposit-box number in which Gautham finds a preserved rice sample.
After escaping another murder attempt in a parking lot, he eludes the police and the two men with Sameera and Singh's help. One of the men, apparently a fan, seeks revenge for his father (one of the other murderers, according to the aged taxi driver), who was killed by Gautham in Belfast when he performed there. Gautham learns that the aged taxi driver he met previously is a businessman and the murderer; the person hit by the businessman's car in Gautham's presence was the actual, innocent taxi driver.
Gautham and the businessman confront each other, and the businessman says that he and Gautham's father were good friends and fellow scientists. They worked on cultivating Golden rice, a variety which could grow in any weather. When Gautham's father refused to sell it in favour of distributing it globally for free, the businessman and Rosarios killed his parents. When he refuses to tell Gautham about his parents, Gautham kills him.
On his way to the airport, Gautham passes the school he had attended and hears children singing a rhyme. It reminds him of a similar rhyme he learned from his mother, and he remembers his way back to his house. At his house (a dilapidated villa) Gautham finds a photo of his parents, Chandrasekhar and Kalyani. He later introduces the rice variety at a global convention as 'the second green revolution', and the film ends with Gautham standing in his field of Golden rice.