Krishna (Vikram) is mentally retarded and has the mental ability of a six-year old. He lives a peaceful life in the hill station of Ooty. He is cared for by Victor (Krishna Kumar), the owner of a chocolate factory where Krishna works. One day he excitedly announces to the village that he will become a father. That night, his daughter is born, but his wife Banumathy dies during childbirth. Unable to grasp the concept of death, he simply accepts that his wife has "gone to God" and starts life as a father. He names his daughter Nila, and raises her with love and care. She soon grows into a happy young girl (Sara). With the help of Victor and his other mentally challenged friends, Krishna enrolls Nila in school.
Nila adjusts herself to school life, and befriends the correspondent Shwetha Rajendran (Amala Paul), who develops a maternal bond with the girl. But when she learns that Nila is Krishna's daughter, she refuses to let her stay with him. Soon a scuffle starts between Krishna and Shwetha's fiancé Karthik (Karthik Kumar). It is broken up by the entry of Shwetha's father Rajendran (Sachin Khedekar) who reveals that his other daughter was Banumathy, who became estranged from him by choosing to marry Krishna. He offers to take Krishna and Nila with him and claims that they are part of his family. Victor agrees and sends them with Rajendran.
At a distance from Chennai, Rajendran tricks Krishna into exiting the car, and abandons him. Distraught, Krishna wanders around the city asking passerby where Nila is. He eventually arrives at a court, where he meets lawyer Vinod (Santhanam) who assumes that he is rich, and promises him that his boss will defend him. He introduces him to his boss/colleague Anuradha Ragunathan aka Anu (Anushka Shetty), who is hesitant to take up the case as she believes Krishna to be a lunatic. But soon, Victor arrives and explains Krishna's predicament, and, moved to tears, Anu agrees to help him.
She files a case against Rajendran, but loses hope when she learns that Rajendran's lawyer is Bashyam (Nassar), a feared senior lawyer who has never lost a case. The case is then heard in the high court, with both party arguring to the custody of the child.
Finally, Bashyam asks Krishna about how he can raise his daughter then to support her financially. Then after a quick show of father-daughter connection and affection, Bashyam withdraws and loses the case voluntarily. Giving Krishna his custody of his daughter, Bashyam leaves the court. After spending some time with his daughter, Krishna then takes her back to Shwetha, so that she will be raised financially stable and that she can become a doctor when she grows up.