On the evening of the Kennedy assassination, Jim MacLaine (David Essex) visits his friend Mike Menary (Adam Faith) at the funfair where Mike works. Jim tells Mike he’s joined a touring rock group called the Stray Cats and invites Mike to come along as their road manager, pointing out that Mike could make millions if the group succeeds. Mike accepts and proves to be a shrewd operator, arranging a better van, accommodations, and a recording session for the group. Privately, Mike tells Jim that arrogant singer/ guitarist Johnny (Paul Nicholas) must go in order for the band to be a success. Largely through Mike’s efforts, the Stray Cats have their first hit single with a song sung by Jim, even though it was released as the B-side to a song sung by Johnny. Jim becomes the new center of attention for fans and press, causing the jealous Johnny to leave the band.
The Stray Cats embark on a successful tour of the USA, where they meet their new manager, Porter Lee Austin (Larry Hagman), a wealthy Texan who has bought a majority financial interest in Jim and the group. The other Stray Cats, especially drummer J.D. (Keith Moon), are frustrated at being ignored while Jim, promoted by Porter Lee and Mike, becomes the focus of media attention. Jim, supported by his new girlfriend Danielle (Ines Des Longchamps), objects to Porter Lee’s treatment of him and his music as a commercial commodity.
Jim’s mother suddenly dies, and Jim, Danielle and Mike return to England for her funeral. There, Jim sees his wife Jeanette (Rosalind Ayres) (whom he abandoned, but never bothered to divorce) and his young son. Jeanette wants nothing further to do with Jim and is living with another man, who has stepped into the father role for Jim’s son. The funeral is mobbed by Jim’s fans and Danielle is upset that Jim never told her he was married.
Back in the USA, J.D. and the other Stray Cats inform Jim they are severing ties with him, leaving him as a solo act with no close friends except Mike and Danielle. Jim embarks on an ambitious project to compose and sing a progressive rock opera glorifying women, in honor of his late mother. When Danielle clashes with Porter Lee and then insinuates Mike is sexually attracted to Jim, Mike arranges for her to catch Jim having sex with another woman, causing her to walk out. Jim’s rock opera, broadcast live to a worldwide audience of millions, is a huge success, but Jim, tired of his rock star life, moves to an isolated castle in Spain and becomes a recluse. Mike, who by now is acting as Jim’s handler and caretaker, lives with him, but old resentments between the two soon surface.
After two years, Porter Lee pushes Jim to come out of seclusion in order to make money to cover unpaid taxes and avoid being forgotten by his public. A major live television interview is planned, but on the day of the interview, the mentally fragile and drug-addled Jim refuses to come out of his room. Mike, whose friendship with Jim has deteriorated, coldly orders him to come out and do his job. Jim finally emerges and starts to do the interview, but gives rude responses and then starts to laugh uncontrollably. Mike, the only one to realize that Jim has overdosed on drugs, rushes to call an ambulance, but Jim dies on the way to the hospital.