In 1983 London, Will, a privileged, gay, sexually irresistible 25-year-old, saves the life of an elderly aristocrat who has a heart-attack in a public lavatory.
To avoid death duties, that grandfather has already settled most of his estate on Will, who therefore has substantial private means and no need of work.
Whilst cruising in a London park, Will enters a public toilet to find a group of older men cottaging.
The novel by Firbank echoes themes central to The Swimming-Pool Library: secrets and discretion; extreme old age, colonialism, race and camp; the sense of deeper truths residing behind a thin façade of artifice.
Charles's house is filled with memorabilia and books; there are homoerotic paintings as well as a portrait of a beautiful African boy.
Charles's early life vividly illustrates themes central to the experience of being homosexual, privileged and British.
Charles becomes aware that he is strongly attracted to black men when he is openly propositioned by an American soldier.
Charles has sex with one of them; a young man who feels insecure about his (comparatively) modest background and sexual inexperience.
As a young man, Charles enters the Foreign Service and travels to Sudan to act as a regional administrator.
He is enchanted by the land and powerfully drawn to African men but finds himself cut off by race, rank and position.
On the way to a boxing club financially supported by Nantwich, Will has an unpleasant encounter with a working class boy, who offers him sex for money.
From the diaries, Will learns that Nantwich has been to Egypt and then returned to London, where he met with Ronald Firbank: an extraordinary portrait of effete decrepitude, camp and alcoholic.
Will takes Phil to visit Staines, a successful studio photographer who echoes Cecil Beaton.
Returning, he encounters a group of skinheads who demand his watch, attack and queer-bash him, destroying the Firbank novel and breaking Will's nose.
It transpires that Staines and Nantwich are collaborating on the production of a pornographic film in which Abdul and the two youths are performing.
It appears to be a case of entrapment, with an undercover police officer soliciting sex from homosexual men.
The African man whom he loved gets married and Charles begins to visit anonymous sex clubs and cruisy bathrooms.
While Charles is in prison, he learns that Taha, the African man, has been beaten to death in an incident that is apparently racially motivated.
Will accepts until he finds that the man is obsessed with gay pornographic conventions, costumes and sex toys.
Disoriented, he leaves and wanders to James's and then the Corry, where Charles Nantwich reveals his designs in giving Will the diaries.
Will and James go to Staines's to see a film, not a piece of pornography but an archive recording of Ronald Firbank in old age.
In 1988, Edmund White called it, "surely the best book about gay life yet written by an English author.