I haven't read any of Hollinghurst previous novels, but I've been told they involve contemporary gay men having lots of sex, and therefore you may not feel comfortable reading them on the subway. At his Bookcourt reading for "The Stranger's Child," he used the phrase "uncharacteristically restrained" in response to a question about the lack of detailed action on the pages of this book. But there is plenty going on between the chapters and sections and after a while that becomes the point.
The story begins just before the outbreak of WWI and focuses on two families who initially come together when two Cambridge students meet and start a secret affair. Cecil Valance is a rather mediocre poet who is aristocratic and charming enough to make up for it, and George Sawle is from a more modest family and apparently never had any friends before. When Cecil visits the Sawle's mere two-acre estate, George's family is too surprised that he has a friend from an impressive family to notice any signs of greater intimacy between them. George's younger sister Daphne is entranced by Cecil and his not-very-good poetry; he awkwardly makes a move on her too and then writes a poem in her autograph book. This poem is later published and becomes known as a WWI poem, and in the ensuing years, there are people who are interested to know the full story behind it and Cecil himself. The book jumps forward decades at a time until the point there are no direct connections to either the poem or its writer surviving.
As the reader, you know just enough to know what other people do and don't know. At times you even know how close they are to possibly knowing what they want to know. Yet there's a lot that happens in those spaces between sections, and there are characters who have no interest in remembering for you (or they have just spent too many years drinking heavily to be able to recall). In the end no one can really know what happens between two people in private, and those histories, even when physically documented, are startingly easy to lose over the passage of time.