The film opens in UK where Colonel Viren Nanda (Jimmy Shergill) goes to meet a wanted terrorist Omar Zafar (Danny Denzongpa) in his holding cell. As Viren informs Zafar that he will be extradited back to India for his crimes, Zafar’s men enter his holding cell, led by Hamid Gul (Jaaved Jaffrey), killing all guards around them, with Zaffar then killing Viren by shooting him and then burning him. As Zaffar escapes in a helicopter waiting on the roof, he puts a $5 million reward for someone to steal the Koh-i-Noor diamond from the Tower of London, but with one condition – the thief must be Indian, to hold up a new extradition treaty between India and UK. Soon after, a man named Rajveer Nanda (Hrithik Roshan) steals it, and when Zaffar’s men are informed of the theft, they travel to Rajveer for the deal. Although they initially travel with the $5 million reward, Rajveer informs them that he now wants $20 million for the deal. Following the disdain of the comment made by Rajveer, a fight breaks out between Rajveer and Zaffar’s men after which Rajveer flies away. After Rajveer escapes, a CCTV footage of him is captured, showing that he is in Shimla. Following Rajveer’s escape, he sees Harleen (Katrina Kaif) sitting in a restaurant, who is there waiting for her internet date, “Vickie”, to show up. Rajveer enters the restaurant posing as “Vickie” and woos her over. He convinces Harleen to use the bathroom and while she is in there, Rajveer fights the remaining men and leaves the restaurant, much to the dismay of Harleen. As she drives home, Harleen accidentally runs over Rajveer, who asks her to stitch up a gunshot wound sustained during the fight. Rajveer then gives Harleen drugged water, with her complying with what he says about the government officials, informing her about where to find guns underneath car seats and what they will say about him.
The next day, the government officials with Zorawar (Pawan Malhotra) visit Harleen at her bank and threaten her to come with them. They tell her that if she does not accompany them, then they will reveal everything to her colleagues. Harleen decides to go with them to the police station. In the car, Zorawar tells her that they are not going to the station but they are taking her to a safe place instead. Harleen remembers about the gun that Rajveer had told her of. She engages the other official in small talk and finds the gun. She threatens both the officers to stop the car and let her go. At the same time, Rajveer appears on a bike and a chase sequence ensues. Both Rajveer and Harleen find a car and escape. When Rajveer goes out to shoot the goons, Harleen escapes and then bumps into her boss, Karan. She tells him about Rajveer and how random people are firing at her. Rajveer follows her. Karan tries to protect Harleen from Rajveer. He annoys Rajveer and gets shot by him in the leg. Harleen is exasperated but leaves with Rajveer again lest he shoots any more people.
In the car, Harleen and Rajveer get into an argument. Harleen states that she wants to go home and that she did a huge mistake by trusting him. Rajveer angrily decides to let Harleen go and hands over the car keys to her. He tells her that he has no other motive than protecting her. She feels guilty and decides to stick to him. They begin to drive again in silence. Rajveer checks a location on his phone which Harleen notices. He then tells her that he has not killed an innocent person before this and does not want her to die. He tries to convince her to come with him for dinner.