The Funny Girl of the novel's title is Sophie Straw, nee Barbara Parker, who decamps from Blackpool in 1964 to become a comedy star in London. She lucks into an audition for a BBC comedy show with serious problems; rather miraculously, the writers and producer listen to her input and they end up with a hit show--Barbara (and Jim)--that runs for four years.
Besides Sophie/Barbara, the novel has four other important characters. Her co-star Clive is a shallow twit who has trouble separating his character from himself. Writing partners Tony and Bill first met in jail, picked up for soliciting gay sex while doing their national service. Since then, however, Tony has married (albeit not entirely successfully on the sexual front) while Bill leads the life of a gay man in a Britain where homosexuality is a crime. The fourth member of the team is Dennis, the producer/director of Barbara (and Jim).
Barbara (and Jim) is based on the notion of class conflict--Barbara is a northern working class girl while Jim is a well-educated Londoner who works for the Labor prime minister. Tony and Bill spend hours trying to figure out how to wring humor from that situation once the novelty has worn off. Meanwhile, Dennis must defend the show's "low-brow" humor from attacks by high culture mavens.
Not all that much really happens in Funny Girl and the book doesn't explore the themes it sets out in any depth. It's a feel-good, almost sentimental book featuring Hornby's humor and excellent dialogue. Not Hornby's best by far, but if it's not made into a movie, I'll be very surprised.
Years later, Tony would discover that writers never felt they belonged anywhere. That was one of the reasons they became writers. It was strange, however, failing to belong even at a party full of outsiders.