The story revolves around two childhood friends Arjun (played by Ajay Devgan) and Mannu (played by Salman Khan) who have some music lineage in their family history. Arjun dreams of being on stage as a performer in the music industry, to live up to his grandfather’s unfulfilled ambitions. Mannu however has little interest in his music tutor father’s instruments and is content with remaining a child at heart with a simpleton attitude.
Through the course of the film, Arjun diligently pursues his dream, at one point almost leaving an uncle who is his only family. He finally makes it to London where he believes he can succeed.
Arjun creates a fledgling band with Zoheb and Wasim (Rannvijay Singh and Aditya Roy Kapoor respectively), two brothers who duped their relatives in Pakistan to travel to London in pursuit of their musical aspirations. He also brings aboard Priya (played by Asin), a music enthusiast from a conservative South Indian family. The other protagonist of the movie, Mannu, is shown to be trying to make his livelihood by playing as a wedding band performer at the village back in India.
Arjun eventually invites Mannu to London to complete his band contrary to his own belief that the latter could create competition within the band.
Upon forming the band, Mannu is shown to have musical talent and the qualities of an entertainer. He therefore becomes popular with the audiences with his unique style of performing. This is in contrast to the earlier part of the film where Arjun struggles to captivate the attention of the crowd despite the music.
Arjun starts feeling envious of the rising success of Mannu. As a further extension of the jealousy, Arjun who is starting a budding relationship with Priya starts sensing that she is now smitten by Mannu. While the latter now starts a relationship with Priya, he does become the target of Arjun’s frustrations who seeks to sabotage Mannu’s career. Zoheb, who doesn’t like Mannu, decides to help Arjun.
The band embarks on a three-city tour spanning Paris, Rome and Amsterdam. Here Arjun deceives a naive Mannu into a rollercoaster ride of promiscuous sex and illicit drugs. He tricks him, gets him addicted to drugs, and then gets him arrested in a car full of them. While pretending to help Mannu, Arjun leaks the drug story to the press. As the three-city tour concludes, the band heads to London to perform at Wembley Stadium in front of an audience estimated at 90,000 (which is of significance since, earlier in the movie, the viewer is told that Arjun’s grandfather had failed before a similar audience). Knowing how important this is for Arjun, Mannu tries to give up drugs. But Arjun decides that his success and Mannu’s total failure are related. He pays a girl to have sex with Mannu, which makes Priya break up with Mannu. In this fragile state, Zoheb pushes Mannu toward drugs again so that he can’t come on stage.
In the moments leading up to the stage entrance, Mannu comes to senses and chooses the righteous path and runs to support his mate. But Arjun, who has become incensed with the crowd chanting Mannu’s name, confesses his envy of Mannu’s talent and what he did to finish Mannu off. The audience boos Arjun, the band breaks up and a sad Mannu goes back to his village.
Arjun’s uncle (Om Puri), advises him to apologize to Mannu. In the village, however, Mannu tells him not to apologize saying that it was his fault that he didn’t see Arjun’s sorrow. They get back together and London Dreams becomes a successful band again.