Rugged and realistic, this intense drama delves into the life of Guddu and Charlie (Shahid Kapoor), identical twins who grew up on the streets of Mumbai. Both have a speech impediment—Charlie has a lisp while Guddu stutters in his speech. The film begins with Charlie narrating that he and his brother cannot agree about anything, and that he believes in taking shortcuts to fulfill his dream of becoming a bookmaker at the racecourse where he works for three criminal brothers who fix races.
Charlie is especially close—closer than he is to Guddu—to the youngest brother Mikhail (Chandan Roy Sanyal). Charlie is double-crossed by a jockey when he bets INR100,000 (US$1,700) on a horse during a fixed race, losing all of his savings. Craving revenge, Charlie locates the jockey in an upmarket city hotel.
At the same hotel, corrupt policemen Lobo and Lele kill three drug dealers and collect a guitar case containing cocaine, which they must deliver to drug lord Tashi (Tenzing Nima). Charlie and his aides invade the jockey's hotel room, take his possessions and assault him. The jockey's aide returns and hands him a gun, leading to a gunfight and foot-chase to the hotel car park, where Lobo and Lele are placing the guitar case in their van. Charlie and his aides seize the van to escape from the jockey's men and realise they have stolen a police vehicle. Charlie drives to a remote location where he discovers the cocaine. Thinking this will lead to his dreams, he steals the guitar case. The policemen find the van, discover that the cocaine is missing and set out to find Charlie.
Meanwhile, Guddu's lover Sweety (Priyanka Chopra) reveals that she is pregnant with Guddu's child, that she is the sister of crooked politician Sunil Bhope, and that she must marry Guddu immediately. They are married later that night. Bhope hears about his sister's actions and sends his cronies to apprehend the lovers. Bhope's men gatecrash the wedding celebrations and beat up Guddu, then realise that he is a migrant from Uttar Pradesh. This enrages Bhope, who orders his men to kill Guddu and return Sweety to his house so he can arrange a marriage for her. Sweety fights off her brother's henchmen and escapes with Guddu.
Charlie tells Mikhail about the cocaine; they are both overjoyed at the money it would make them. When Charlie returns to retrieve the case, Bhope and his men are waiting inside the van. One of Bhope's men recognised Guddu as Charlie's twin brother and Bhope demands that Charlie reveals Guddu's whereabouts. Mikhail, who is drunk, interrupts their conversation and is killed by Bhope.
On the way to the airport, Guddu realises that Sweety has faked her identity. At a petrol station, Lobo and Lele notice the pair; they mistake Guddu for Charlie and arrest him. They assault Guddu and refuse to believe that he is Charlie's twin brother until Guddu's mobile telephone rings. The call is from Charlie's number and Bhope is on the line. Lobo, Lele and Bhope agree to exchange Charlie for Guddu and Sweety on a train. The policemen take Guddu and Sweety to Bhope's house, where Bhope reveals that a local builder will pay him INR50 million (US$830,000) to marry Sweety to the builder's son. Guddu bargains with Bhope—if he retrieves the cocaine-filled guitar case for Bhope he will get Sweety. Bhope sends his henchmen with Guddu to retrieve the guitar case from Charlie's house.
The policemen, desperate to recover the cocaine, assault Charlie, who refuses to negotiate, realising that the policemen are in as much trouble as himself. One of the policemen shoots himself in the thigh; Charlie takes them hostage and negotiates with Tashi to exchange the guitar case for INR1 million (US$17,000). Charlie sends the injured policeman and his aide to deliver the details to Tashi and returns to his house to retrieve the cocaine. At Charlie's house, Guddu arrives with Bhope's men, unaware that Bhope has ordered them to kill Guddu once they have the case. Sweety hears about this and shoots at the members of her household. Guddu finds the case and he fights with Charlie, who lets Guddu go. Guddu takes the cocaine to the police, who bug him. Guddu arrives at Bhope's house at the same time as Tashi and his gang, with Charlie as their hostage. Bhope and Tashi negotiate to trade the drugs, but Charlie snatches the guitar case and threatens to destroy it if Guddu and Sweety are not released. The lovers escape as the police arrive, leading to a shooting spree in which the cocaine is destroyed. Charlie's bosses arrive looking for vengeance for the murder of Mikhail, but are killed along with Bhope, Tashi and their henchmen. Charlie is shot and wounded.
Sweety gives birth to Guddu's twins and Charlie opens a bookmaking counter at the racecourse. Charlie is engaged to Sophia, an elegant woman who featured in his dream at the beginning of the film.