I nominate A Question of Upbringing by Anthony Powell.
Relatively short at 181 print pages, it's the first book from A Dance to the Music of Time.
A Question of Upbringing (1951) introduces us to the young Nick Jenkins and his housemates at boarding school in the years just after World War I. Boyhood pranks and visits from relatives bring to life the amusements and longueurs of schooldays even as they reveal characters and traits that will follow Jenkins and his friends through adolescence and beyond: Peter Templer, a rich, passionate womanizer; Charles Stringham, aristocratic and louche; and Kenneth Widmerpool, awkward and unhappy, yet strikingly ambitious. By the end of the novel, Jenkins has finished university and is setting out on a life in London; old ties are fraying, new ones are forming, and the first steps of the dance are well underway.
Anthony Powell’s universally acclaimed epic A Dance to the Music of Time offers a matchless panorama of twentieth-century London.
"Anthony Powell is the best living English novelist by far. His admirers are addicts, let us face it, held in thrall by a magician."—Chicago Tribune
"A book which creates a world and explores it in depth, which ponders changing relationships and values, which creates brilliantly living and diverse characters and then watches them grow and change in their milieu. . . . Powell's world is as large and as complex as Proust's."—Elizabeth Janeway, New York Times
"One of the most important works of fiction since the Second World War. . . . The novel looked, as it began, something like a comedy of manners; then, for a while, like a tragedy of manners; now like a vastly entertaining, deeply melancholy, yet somehow courageous statement about human experience."—Naomi Bliven, New Yorker
“The most brilliant and penetrating novelist we have.”—Kingsley Amis
“There is no other work in the annals of European fiction that attempts meticulously to recreate half a century of history, decade by decade, with anything like the emotional precision or details of Powell’s twelve volumes. Neither Balzac’s panorama of the Restoration, nor Zola’s chronicles of the Second Empire, nor Proust’s reveries in the Belle Epoque can match a comparable span of time, an attention to variations within it, or a compositional intricacy capable of uniting them into a single narrative. . . . The elegance of this artifice was only compatible with comedy.”—Perry Anderson