Robust pleasure lies on nearly every page of Alan Hollinghurst's novels, including his sixth and latest, "The Sparsholt Affair." Turns of phrase, paragraphs, whole scenes deserve to be read a second time.

A hero to many gay readers I know for his sexually frank 1988 debut, "The Swimming Pool Library," Hollinghurst has released a novel every five or six years since then, and he remains a must-read creator of witty, socially engaged, artfully imagined and realized fiction.

Still, his last two novels also have left me occasionally bored, frustrated or annoyed.

Brilliant out of the gate and energetically rendered in a wonderful final section, "The Sparsholt Affair" sags in the middle. Big time jumps, narrative gaps and a large cast make it a chore to track who's who and which decade we are in. We don't mind doing some heavy lifting, so long as there's a payoff, but enticing early characters and plot lines are abandoned entirely, sometimes replaced by stories less appealing.

The novel opens as young David Sparsholt, athletic and handsome, incites lust among several male members of a student literary club at Oxford in 1940. That Sparsholt is straight and affianced doesn't faze his stalkers. Peter Coyle paints him nude, and Evert Dax, son of a famous writer, beds him one night, or says he did.

The wartime mood of Oxford is beautifully evoked, especially in a nocturne where narrator Freddie Green and Sparsholt volunteer together atop the Oxford Bell Tower on dusk-to-dawn fire-watching duty. "When the moon, in its last quarter, had slipped down behind Merton tower, the whole city would sink into mere muddled shadow, as if a vast grey net had been thrown over a table heaped with once familiar objects."

After having "a good war" as an airman, Sparsholt prospers as a manufacturer. He and his wife have a son, Johnny, who replaces David as the novel's main character for the duration of the book, which ends in 2012.

The "Affair" of the title, with its whiff of a juicy tabloid scandal, is never detailed, although David Sparsholt may have traded sex with an elected official for lucrative government contracts. We learn only that there was a criminal trial, negative headlines in the papers, and that Johnny's parents divorced.

Johnny, who is gay, becomes a dad when he donates sperm to two lesbian friends. He has a career as a portrait painter that brings him into a London social circle that includes the now dissolute or watered-down chaps who knew his dad at Oxford. Hundreds of pages later, David — and that old painting of him — reappear when Johnny tries to bond with his aging father after a long estrangement.

A warm, funny final section has Johnny, 60 and single after the death of his longtime partner, dancing the night away at a gay club with a friend. He meets a much younger man and gets news by cellphone of his father's death while in the disco's lavatory.

Despite being sometimes blocky and circuitous, "The Sparsholt Affair" uses its big time span wonderfully to contrast the secretive, mostly hidden and shameful same-sex encounters of David with Johnny's life in a much more open gay culture. The novel has intriguing things to say about changing father-son relationships. I wish it had said more.

Claude Peck is a former editor at the Star Tribune.

The Sparsholt Affair
By: Alan Hollinghurst.
Publisher: Knopf, 417 pages, $28.95