Naani is a mischievous eight-year-old boy who is always troubling his mother. His mother scolds him for his behavior, such as when he eats toothpaste or urinates in bed. Naani falls down on a road one day and a young woman helps him. Naani's elder brother plans to watch a movie with his friends in the absence of their parents and Naani demands to join him, which his brother does not allow. Angered, Naani cuts off the power which creates a short circuit at home. Naani's mother scolds him and shouts at her husband for not stopping with one child. This hurts Naani and he runs away from home to jump into a river. But he is stopped by an old man who takes Naani to his place. The old man introduces himself as a scientist who has his own laboratory. He insists that Naani help him in his research. Naani agrees and the scientist uses his research to transform him into a young man. Naani starts to live as a young man physically, but remains a child mentally. He stays away from his family. The only person other than the scientist who knows the truth is his child friend. Naani meets a girl (Priya) at a park who helped him once when he fell down. Naani helps remove dust from her eyes, smiles at her, and leaves. The girl is attracted to him and looks for him.
Naani goes for a job interview at a toy manufacturing company. The owner who interviews him demands that he have childhood memories and be like a child to understand children's tastes. Naani grabs the job easily. The company falls into the hands of the owner's daughter who turns out to be Priya. Priya is happy to see Naani in her company. Their friendship makes Raj (another employee) jealous. Naani overcomes Raj's idea for a new type of bed for kids and introduces his own idea. Naani meets his brother as an anonymous man and hears that his mother is depressed over Naani's disappearance. Naani meets his mother who had fallen ill. Naani asks the scientist to change him back. The scientist complies and Naani reconciles with his mother. That night he changes back into the young man, shocking the scientist.