Prem (Ranbir Kapoor) is a free-loader who, while helping his friend elope, meets Jenny (Katrina Kaif). They both share the trait of developing a stammer when they are emotional.In such a moment, the stammering Jenny induces a spontaneous stammer in Prem, which she misunderstands for mockery.Although this makes her dislike Prem initially, when she finds out his stammer is authentic, the two become friends. Prem's feelings eventually blossoms to love, although Jenny is oblivious to this and only considers him a friend.When he tries to tell Jenny his feelings, he finds out that Jenny is in love with her college friend Rahul (Upen Patel). On her wedding day to Tony (Pradeep Kharab), who her parents force her to marry, Prem helps Jenny escape.

He then meets Rahul and finds out that Rahul loves Jenny more than his family, so helps them board a train to escape. However, Rahul disappears at the train station, and Jenny returns to Prem so Prem can help her find Rahul.

As Rahul's father does not like Jenny and completely opposes relationship between Jenny and Rahul, mainly due to the religious barrier,Jenny being a Christian and Rahul a Hindu, when Prem visits Rahul's house for Jenny's proposal with Rahul, he is insulted by Rahul's father.Prem convinces his mother to let Jenny hide in their house while Rahul's family search for her, but they are eventually caught by the police. After that, Jenny lies to the police, claiming that she and Prem are in love, to save Rahul's name.While Prem corroborates Jenny's lie, he gets emotional and spurts out his true feelings for Jenny, which Jenny mistakes for over-acting.

Prem and Jenny successfully go to the club to get reunited with Rahul. Rahul tells Prem that he (Rahul) and Jenny are going to prepare the wedding in two days.

Unfortunately, a day before the wedding, Jenny gets kidnapped by Sajid Don (Zakir Hussain) who is seeking a ransom from Rahul's father in exchange for her.Prem and his buddies find her in Sajid Don's warehouse. A hilarious fight ensues between Prem and Sajid Don's gang. Prem's father (Darshan Jariwala) joins the fight, too. Later on, Sajid Don, a wanted criminal, gets arrested.

Rahul and his father, who's running for the elections, tell the media that it was they who were the ones involved in the fight with Sajid Don, intending to buy a good name for Rahul's father before the elections. On Jenny and Rahul's wedding day, Jenny finds out that Prem actually gave consent to Rahul and his father to publicize their false story. This and past recollections of Prem's selfless caring for her, makes her realize that she truly loves Prem and that Rahul and his family are actually very selfish, and prompts her to become a runaway bride. She is united with Prem and the two happily get married, in a small celebration at a marriage registration office.

Indian-born Manmohan Malhotra (Rishi Kapoor) re-located to London, England, established himself, returned to India, got married to Bebo (Nina Wadia), and after four years got a visa for her so that she could live with him. Shortly thereafter, she gave birth to Jasmeet (Katrina Kaif). Manmohan was always embarrassed by Bebo as she was fat and could not speak English. As a result, he always left her out of important occasions, while he socialised. Bebo did not want Jasmeet to end up like her, so she got her educated in an English school, encouraged to mingle with British friends, and Jasmeet was transformed into Jazz – a beautiful young woman, modern in looks, talk, habits, and heart.

Her father had set her to meet a young lad, Bobby Bedi (Ritesh Deshmukh), though the date turns out to be a disaster and Bobby rejects her. Manmohan thinks that it is impossible to get him an Indian son-in-law, although his friend, Parvez Khan (Javed Sheikh), is in a similar situation with his son, Imran (Upen Patel), who has a blonde girlfriend, Susan (Tiffany Mulheron). Manmohan takes his family for a tour in India and forces Jasmeet to marry Arjun Singh (Akshay Kumar).

On their return to London, Jasmeet announces that she is getting married to Charlie Brown (Clive Standen), who is well educated and has good friends and connections, even with Prince Charles. She refuses to recognise her marriage with Arjun as there is no proof of the wedding. When Jasmeet is introduced to the friends of the Brown family, she is subjected to considerable racist abuse (snake charmers, Indian rope tricks, tandoori chicken) as well as a quote from Winston Churchill: 'When we leave India, the country will be in the hands of goons'. During this period, Jazz becomes close with Arjun who still supports her. Charlie Brown then has a rugby match against the Indians and Arjun, the English lose and Brown is verbally racist to the Indians. Imran is then asked by Susan's parents to leave Islam, become a Christian, change his name to Emmanuel or Ian, as well as provide written proof that his family is not associated with terrorists. The film ends on a happy note when Imran decides not to be a Christian and Susan is accepted by Imran's family; Jazz realises her love for Arjun, runs away from her wedding to Charlie Brown, and goes with Arjun back to India where they are seen riding Arjun's motorcycle. While they are on the motorcycle Arjun reveals that all along he knew how to speak English.