Rock On begins in Mumbai, with the rock band "Magik" in 1998. Aditya Shroff (Farhan Akhtar) is the lead singer who rebelled against his well to-do family to play music. Joseph (Joe) Mascarhenas (Arjun Rampal) is the lead guitarist who feels he has to prove his worth as a musician. Rob Nancy (Luke Kenny) and Kedar Zaveri or KD/"Killer Drummer" (Purab Kohli) comprise the remainder of the band. They are in their early twenties, young, wild and carefree, and only think about succeeding in the music business. After a competition is announced, specifically for Indian rock bands, to be organised by Channel V, they decide to enter it as the winner will be offered a contract for an album and at least one music video.
While they win the competition, they must make a number of compromises when signing the contract. This creates tension within the band. Joe feels the most slighted as his song is not included (making way for a remix of a random wedding song to capitalise on the upcoming "wedding season"). In addition, his girlfriend, Debbie (Shahana Goswami), an aspiring fashion designer, is rejected as the band's stylist. Later, when the cameramen focus solely on Aditya during the filming of the music video, Joe becomes furious and lashes out at Aditya before marching out of the studio with Debbie. Aditya, who had failed to notice anything was amiss, is shocked and decides to leave as well. He packs his stuff, writes a note breaking up with his girlfriend Tania (Nicolette Bird), and leaves for Delhi. "Magik" thus disbands and its members, once the closest of friends, become estranged from each other.