Software engineer Shekhar Subramaniam (Shah Rukh) is a computer geek who designs video games. Meanwhile fashion conscious Sonia (Kareena) is Shekhar love interest with no concern about technology and computers.
Sonia has an 8 year old son who has already given up on Shekhar because he is not 'cool' enough.
So Shekhar tries every trick in the book to woo him back. Just when Shekhar and the young lad hit a deadlock, the geek strikes gold by designing a special video game.
But all hell breaks loose when the game that was meant to be played starts playing them!
Shekhar turns into a video-game hero, G.One taking on his self-created techno-monster Ra One (Arjun Rampal). Ra One is said to mean Random Access-Version One.