Koi… Mil Gaya is the story about Rohit Mehra (Hrithik Roshan) who shows the world that friendship is truly universal.

Sanjay Mehra (Rakesh Roshan) is a scientist obsessed with establishing contacts with extraterrestrial life. He invents many innovative gadgets, instruments and finally succeeds in devising a computer that can transmit message to space.

His foresight becomes reality when as a response to his signals, a spaceship is sighted in the sky. But before Sanjay can even enjoy his success, he and his wife Sonia (Rekha) meet with a horrific accident where Sonia survives but Sanjay loses his life.

Sanjay's son Rohit is born into this world; a mentally challenged child who faces ridicule and torment at every phase of his life. His lone companion is Nisha (Preity Zinta) whose compassion draws her towards Rohit.

One day Rohit discovered his father's old computer and calls Nisha to help him use it. Both of them are completely fascinated by the images and instructions that appear on the screen and relentlessly experiment with the device; not realizing the impact this would have.

The whole town witnesses a blackout and a bizarre phenomenon… in an incandescent glowing sky… a colossal spaceship is sighted.

However more strange findings are in store for Rohit's town – A pair of footprints not belonging to man or animal are found.

What could this mean?
Who will Rohit and Nisha find?
Is danger lurking somewhere close?
A nation holds its breath.