Raj (Bobby Deol) and Priya (Kareena Kapoor) meet by chance and fall in love after a whirlwind romance. They marry and reside in Switzerland, where they meet another Indian couple: Vikram Bajaj (Akshay Kumar) and Sonia (Bipasha Basu). The couples quickly become friends and decide to go on a Christmas vacation together to Mauritius.
There, Raj sees Vikram with another woman, looking intimate. Sonia begins to try to seduce Raj, who rejects her. Vikram notices Raj looking at Sonia and casually talks to him about wife swapping, this upsets Raj and an argument breaks out between the two men. However, a couple of days later, the couples resolve their issues and become friends again. On Vikram's birthday, the two men get drunk and Vickey asked whether he could become Raj for one day and they go in each other's house. The next morning Raj goes jogging in order to work off his hangover and finds that he cannot recall much of the previous night and thinks about Vicky having sex with priya by sleeping on top of Priya covered in blue bedsheets without any dress or ornaments.
After some time, Sonia is found dead, and Raj is accused of her murder. Determined to prove his innocence, Raj manages to escape from court, and is chased by the Swiss police. He meets Priya, who eventually believes his innocence and aids him in finding out what really happened. He decides to search Vikram's house, only to be interrupted by Vikram, who calls the police and then reveals that everything was planned in advance. Raj escapes in Vikram's car with Priya.
Raj finds a boarding pass that belongs to Sonia Bajaj, which states that Sonia arrived in Zurich on 29 December—however, Sonia was supposedly murdered that night. Raj suspects her to be the woman he saw with Vikram, traveling to Geneva together. In Geneva, Raj meets an insurance officer who is trying to find evidence that Vikram was involved in the death of his wife, in order to receive her life insurance payment of $100 million. Working with the insurance agent, Raj traces Vikram to a cruise ship. There, he sees Vikram dancing with a woman who is revealed to be 'Sonia', alive and well.
In the climax, Vikram explains the whole plan to Raj - the woman he saw in Mauritus was his wife Sonia Bajaj (Mink Brar), while the woman with him that Priya and Raj were introduced to in Switzerland is his girlfriend Neeta (Bipasha Basu). Vikram, a struggling musician, married the wealthy and glamarous Sonia, and convinced her to take out an insurance plan of $100 million on herself. He then formulated a plan with Neeta to have Sonia killed so that they could collect the money.
In a turn of events, Raj takes Vikram to a computer and shows him his empty bank account. Raj tells him that he had guessed his password, "Everything is planned", something that Vikram used to say a lot, and used it to transfer the money back to the insurance company. Raj also reveals that everything Vikram said had been recorded. A fight erupts between the two and Neeta dies in the conflict. Angered at losing Neeta, Vikram gets aggressive, killing the insurance officer and seemingly kill Raj. He chases Priya to kill her, too, but Raj is able to save her. Vikram dies when he is impaled by an anchor. Now proved innocent, Raj and Priya move back to India.