expensive movie ^^

Jenny Nayar (Shahana Goswami), an employee of the UK-based company Barron Industries, introduces a new technology that allows objects from the digital world to enter the real world. Shekhar Subramanium (Shahrukh Khan), who also works for the company and has delivered a spate of commercial failures, is given a final chance to devise a video game which will actually succeed. In order to impress his skeptical son Prateek (Armaan Verma), and upon the request of his wife Sonia (Kareena Kapoor), Subramanium uses his son's idea that the antagonist should be more powerful than the protagonist.

Shekhar's work colleague Akashi (Tom Wu) provides the motion capture–based movements of the game characters, while Jenny does the programming. Jenny uses Shekhar's face as a model for the face of the game's protagonist (G.One), whilst the antagonist (Ra.One) is faceless. The game, titled "Ra.One", has three levels; either of the players can only be killed in the third level using a special gun that holds a single bullet. While designing the game, Akashi notices malfunctions in the game's functioning but ignores them. When the game is finally launched, it receives a standing ovation and Prateek loves it so much that he insists on playing it instantly. He logs in under the alias "Lucifer" and proceeds to the second level, but is interrupted by Akashi. Ra.One, being unable to end his turn with Lucifer, becomes determined that Lucifer shall die.

When the mainframe fails to shut down, Akashi calls Shekhar, who notices a problem with the game. Ra.One uses the initially introduced technology to enter the real world, kills Akashi and goes to find Lucifer. Shekhar, realizing that something is amiss, rushes home but is blocked by Ra.One on the way. In an attempt to save his son, Shekhar claims that he is Lucifer. However, Ra.One scans Shekhar's I.D. and kills him for lying. Later, Prateek notices the strange circumstances of his father's death and realises that Ra.One has come to life. He and Jenny attempt to bring G.One to life. Meanwhile, Sonia tells Prateek that the family will return to India. Having taken the form of Akashi, Ra.One chases them, but G.One enters the real world through Jenny's computer and causes a gas explosion which saves them and destroys Ra.One. G.One takes Ra.One's H.A.R.T., without which Ra.One is powerless. Sonia realizes she cannot leave G.One and takes him along with them to India using Shekhar's passport. G.One promises Sonia that he will protect Prateek from harm. Subsequently, Ra.One returns to life, takes the form of a billboard model (Arjun Rampal), and goes after G.One and Prateek.

During Prateek's birthday party, Ra.One hypnotises Sonia, assumes her form and kidnaps Prateek. Ra.One then instructs G.One to give him his H.A.R.T. back, and sends the real Sonia in an uncontrollable Mumbai Suburban Railway train. The train crashes into the Chatrapati Shivaji Terminus and destroys it, but G.One saves Sonia just before the crash. He returns to save Prateek. The game resumes, with Prateek controlling G.One. Following a fight, both of the characters reach the third level. With little power left, G.One and Prateek trick Ra.One into shooting G.One without his H.A.R.T. attached, leaving Ra.One helpless. Furious, Ra.One creates ten copies of himself. Prateek, unable to differentiate the real Ra.One, asks G.One to quote one of Shekhar's sayings: "बुराई संग जो मेल रचाया, फिर कभी न छूटे उसका साया" ("If you join the forces of evil, its shadows shall always follow you"). The pair realise that only one of the ten Ra.Ones has a shadow: the original one. G.One shoots and destroys him, and after absorbing Ra.One's remains, transports himself back into the game's world. Several months later, Prateek and Sonia return to the UK, where Prateek finally manages to restore G.One to the real world.