Ever since they were sent into World War I battle in 1918, Sergeant Pepper and his Lonely Hearts Club Band of Heartland, USA, have been spreading the message of joy and love to the world, which has made the band and Heartland famous. Since Sergeant Pepper's death in 1958, the band's instruments have been housed on display at Heartland City Hall as symbols of that love and joy. Before his death, Sergeant Pepper asked his adolescent grandson Billy Shears (Peter Frampton) to form his own band and in order to continue to spread the message of joy and love. With Billy's brother Dougie Shears (Paul Nicholas) as their Manager, Billy, now an adult, and his three best friends, brothers Mark, Dave, and Bob Henderson (the Bee Gees), embark on their lives as a new Lonely Hearts Club Band. The band quickly comes to the attention of Hollywood music producer B.D. Hoffler (Donald Pleasence) Of B.D. (Big Deal) Records. With the boys off to Hollywood to spread the words of joy and love to the world, enter into Heartland the evil and demented Mr. Mustard (Frankie Howerd), an ex-real estate agent who wants to take over Heartland by destroying what made it famous. To do so, he plans to steal the instruments in city hall and promote the music of the Future Villain Band (Aerosmith) in place of the Lonely Hearts Club Band. With Billy's hometown girlfriend Strawberry Fields at their sides, the boys try to thwart Mustard's dastardly plan at their own peril while still trying to spread their own message of love and joy to the world.