Koi... Mil Gaya

A Sindhi Canadian scientist named Sanjay Mehra (played by the film's director Rakesh Roshan) creates a computer from which he dispatches variations of the syllable Om, hoping to attract the attention of extra-terrestrial life. When he finally receives a response, the scientific community mocks him and makes fun of him.

As he is driving home, an alien spacecraft enters the vicinity, then he looks out the window and exclaims: "UFO," and begins to veer off the road. His pregnant wife turns around the steering wheel causing the box car to flip over a stone and explode. His wife is thrown out of the car and Dr. Mehra dies in the car. His pregnant wife, played by Rekha, survives the wreck and decides to return to India. Their son Rohit (played by Hrithik Roshan, who is Rakesh Roshan's son), when born, is developmentally disabled.

His mother raises him with tender care in the town of Kasauli, by which he grows up to be a young man of limited intellect and childish personality, yet with a loving heart. Rohit has a number of much younger friends; children with whom he plays and who are very loyal to him. He also befriends a young lady named Nisha (Preity Zinta). Nisha feels sympathy for him and humors him as one would humor a child, having learned of his mental disability from his mother, who chastises Nisha's suitor Raj for beating Rohit up.

Rohit and Nisha find Sanjay's Om computer and summon the aliens by accident. The visiting aliens leave in haste and one of them is left behind. Rohit, Nisha, and Rohit's young friends find him, befriend him, and name him Jadoo (meaning "Magic" in Hindi and Urdu) when they discover his abilities of psychokinesis. Jadoo's remarkably vast intelligence leads him to discover that Rohit is mentally subnormal, whereupon he uses his magic to enhance the boy's mind. He is now accepted by young-adult society. Only the loyalty of his friends and Nisha prevent him from developing total arrogance. Raj and his sycophants attempt to embarrass Rohit multiple times, only to be beaten in fights as well as in a basketball game, wherein Rohit's bodily strength has increased with his mental calibre.

Nisha and Rohit spend more and more time together, before and after his enhancement; ultimately Rohit proposes marriage to her. She agrees. Jadoo's presence is kept secret from all humans except Rohit's friends and mother.

However, the government has not given up their search for the alien arrival. Police capture Jadoo, who is then rescued by Rohit. Jadoo flees in his returned family's spaceship and apparently takes Rohit's new powers with him. Rohit is again mentally disabled, which saves him from prosecution by the government. Later, Jadoo restores Rohit's special abilities permanently. Nisha and Rohit can now lead a happy life together.