Jonathan Yardley was the book critic of The Washington Post from 1981 through 2014. He is the author of “Our Kind of People: The Story of an American Family,” and other books.

About a quarter-century ago, Vanity Fair published an article about Helen Hope Montgomery Scott, Janny Scott’s grandmother, a larger-than-life figure who was celebrated as “the model or the inspiration” for Katharine Hepburn’s character Tracy Lord in Philip Barry’s delightful and hugely popular play and film, “The Philadelphia Story.” The magazine article, Janny Scott writes, “was humorous, elegiac, and tinged with melancholy,” words that also are exactly right for “The Beneficiary,” her engrossing, lovely but wholly unsentimental portrait of her family and her father.

Scott’s book, like Barry’s play and film, is very much a Philadelphia story, one set not in the city’s historic center but in its Main Line, that string of communities — some downright rich, others merely prosperous — that stretches away from the city to the northwest. Though her story is so crammed with characters that Scott feels obliged to warn that “no reader need keep them all straight,” three are at its center: Robert L. Montgomery (1879-1949), known as “the Colonel,” the founder of the family dynasty; the aforementioned Helen Hope Montgomery Scott (1904-1995); and Robert Montgomery Scott (1929-2005), the author’s father.

This last is the beneficiary of her title, but there were many others: “Land, houses, money: Wealth had tumbled in my father’s family from one generation to the next. Each new descendant arrived as an unwitting conduit for its transmission. You had a right to enjoy it, an obligation to protect it, a duty to pass it on to your own unsuspecting children. It was a stroke of good fortune, of course. But what you could never know, starting out, was how those things would influence decisions you’d make over a lifetime. You might resolve to live as though that wealth didn’t exist, but sooner or later it would probably insinuate itself into your thinking about jobs, profession, marriage, children. Some beneficiaries flourished. Some didn’t. For some, the impact of all that good fortune appeared to have been mixed.”

The center of the family’s life was “a large English Renaissance Revival-style house” built by the Colonel and called Ardrossan, “after a town and a castle in southwestern Scotland left behind by his ancestors.” The property grew to “some eight hundred acres . . . roughly the size of Central Park, located a half hour’s drive from the center of the fourth largest city in the country. It was a nineteenth-century British estate, plucked from the pages of Jane Austen or Henry James, floated across the Atlantic, and wedged in among swimming pools of John Updike and John Cheever. The place . . . comprised dozens of houses, a half dozen barns, stables, carriage houses, garages, silos, an ice house, a root cellar, several swimming pools, tennis courts, a kennel, and a couple of one-room schoolhouses.”

It was money gone berserk, a monument to “the absurdity of things,” a “curiosity, a marvel, an awkwardness, too.” The privileges enjoyed by the Montgomerys and the Scotts derived from only “a middling American fortune — a fortune that would pale by comparison to many, like those of Rockefellers or Carnegies or Kochs, but one sufficient, if shrewdly managed, to subsidize a generation or two,” which is exactly what it did, as the Colonel’s gifts for high finance did not pass down through the family and in time inertia set in.

Nowhere did this prove more true than in the life of Robert Montgomery Scott, a man of great charm (when he chose to turn it on) and deep insecurity. After getting out of law school at the University of Pennsylvania he did this, that and the other with no enthusiasm for any of it until finding himself president and chief executive of the Philadelphia Museum of Art in 1982, in which capacity he became “an admired figure — the civic-minded, public-spirited, socially alert patrician.” A great institution that had fallen on hard times thrived under his leadership: “In his sixteen years’ tenure as CEO of the museum, its attendance climbed to an all-time high. Its endowment increased fivefold. At the hundreds of parties, receptions, and openings all over the city that the museum president might be expected to attend each year, you could find him — face flushed, eyes twinkling, drink in hand.”

That drink in his hand eventually rendered him ineffective and ultimately killed him. What he called “ ‘the problem’ of alcoholism . . . had been passed down on both sides of his family.” In the late 1960s, he was invited by a fellow Philadelphian, Walter Annenberg, to be his special assistant at the Court of St. James, to which Annenberg had been appointed by Richard Nixon as American ambassador. London was “a turning point in my father’s drinking,” Scott writes. There was “sherry before lunch, wine with lunch, port after lunch.” Back in Pennsylvania “after four years in London, he added his British drinking habits to his American ones.” To all intents and purposes he was drunk just about all day and night.

So a story about wealth and privilege unimaginable to most of us becomes, in the end, a sad and cautionary tale. In some senses F. Scott Fitzgerald was right when he wrote that “the rich are different from you and me,” but in the deepest sense he was wrong: They are just as vulnerable to human weakness, insecurity and heartbreak as are any of us, though when they fall they have a longer way to go, and sometimes their fall is presented on a public stage. Reading Janny Scott’s fine book I found myself recalling, over and again, two of the great poems of early-19th-century romanticism. Coleridge, of course: “In Xanadu did Kubla Khan/A stately pleasure-dome decree,” but even more to the point, Shelley:

My name is Ozymandias, King of Kings;

Look on my Works, ye Mighty, and despair!

Nothing beside remains. Round the decay

Of that colossal Wreck, boundless and bare

The lone and level sands stretch far away.

The Beneficiary

Fortune, Misfortune, and the Story of My Father

By Janny Scott

Riverhead. 278 pp. $28