The story revolves around two childhood friends, Arjun (played by Ajay Devgn) and Mannu (played by Salman Khan). When Arjun was 17 years old, he was more focused on becoming a singer but his father disagreed therefore he began praying for his death so he can go to London. The only one who consoled him was his 15 years old friend Mannu. After Arjun’s father dies, he finally travels to London with his uncle (Om Puri) whom he later runs away from after arriving.
Arjun, now 35 years old 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. Back in India, Mannu seduces married women and finds himself in debt with the locals.
After paying his debt, Mannu goes to London to join Arjun’s band, but becomes more popular with the crowds. Mannu also flirts with Priya.
The band embarks on a three-city tour spanning Paris, Rome, and Amsterdam where 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 similarly huge 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 pretend to have oral sex with Mannu, which makes Priya break up with Mannu. In this fragile state, Zoheb pushes Mannu toward drugs again and his mental state is now so fragile that he can’t face appearing 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 show ends in chaos, the band breaks up and a sad Mannu eventually returns to his village.
Arjun’s uncle advises him to apologize to Mannu. Then it is revealed that after knowing the truth Priya and Mannu reconcile. Also, she marries Mannu and lives with him in his village. In the village, however, Mannu tells him not to apologize saying that it was his fault that he didn’t see Arjun’s sorrow and Priya also pardons Arjun for his wrong deeds. They get back together and London Dreams becomes a successful band again.