“On December 28, 1817,” writes Stanley Plumly, “the painter Benjamin Robert Haydon hosts what he refers to in his diaries and ‘Autobiography’ as the ‘immortal dinner.’ The stated reasons for the dinner are, one, that Haydon wants to introduce his young friend John Keats to the great William Wordsworth, and, two, that Haydon wishes to celebrate his progress on his most important and largest historical painting so far, ‘Christ’s Entry into Jerusalem.’ ”

This meeting of the two poets — self-important Wordsworth just past his creative prime, handsome young Keats only starting to write the poems of his too brief maturity — is an iconic moment in the history of English literature. Add the presence of the drunken, whimsical Charles Lamb (who, a few years later, will begin to produce his “Essays of Elia”), a doomed African explorer named Joseph Ritchie, a fatuous government official and the deeply ambitious, self-regarding Haydon himself and you certainly have the makings for, at the very least, a highly memorable evening.

You also have the springboard for this wide-ranging, digressive, lyrical, meditative, repetitive and deeply considered book by poet Stanley Plumly. Do not, in any way, expect “The Immortal Evening” to be a bright, sparkly account of a bright, sparkly dinner party. This is, in fact, an essay on mortality as much as immortality.

Unlike Boswell transcribing Samuel Johnson’s conversation, Haydon never sets down much of what his dinner guests actually said. Wordsworth, he recalls in a diary entry, declaimed Milton “with an intonation like the funeral bell of St. Paul’s & music of Handel mingled,” while Keats apparently recited one of his poems “of Satyrs & Fauns & doves & white clouds.” No witty repartee survives, unless you count Lamb’s repeated singsong of “Diddle idle don/ My son John/ Went to bed with his breeches on,” with which he annoys that “silly” — Lamb’s adjective — government official (who happened to be Wordsworth’s boss).

By necessity then, Plumly heavily contextualizes every element of the evening, starting with several pages about the distances each guest had to walk through London to reach Haydon’s home in Lisson Grove. In alternate sections, he then explores the lives and achievements of the members of the dinner party as well as the forces that brought them together and later split them apart.

“The Immortal Evening: A Legendary Dinner with Keats, Wordsworth, and Lamb,” by Stanley Plumly. (W. W. Norton)

Haydon, perhaps surprisingly, comes to be the dominant figure of the book. Yearning for glory as a history painter, he created huge canvases — “The Raising of Lazarus,” for example — and is now pretty much forgotten. His diaries and autobiography, in fact, are his main claim to modest fame, for they reveal a superbly observant writer of sometimes highly rhetorical prose. Feckless and irresponsible, Haydon ended up in debtors’ prison four times and, finally, feeling utterly superannuated, committed suicide. Change “poets” to “painters” and you might readily apply to him one of Wordsworth’s most famous couplets: “We poets in our youth begin in gladness; / But thereof come in the end despondency and madness.”

In fact, death haunts this book. Plumly reminds us that Lamb lives with and cares for his sister Mary, who, years earlier, stabbed and killed their mother in a fit of insanity. Within a year of the dinner, Ritchie dies of fever while searching for the source of the river Niger. Within a little over three years, a despondent Keats succumbs to tuberculosis in Rome: “I have left no immortal work behind me,” he writes in an 1820 letter, “but I have lov’d the principle of beauty in all things, and if I had had the time I would have made myself remember’d.” (That phrase “if I had had the time” is simply heartbreaking.) As for Wordsworth, by the evening of the dinner, his poetic gift had essentially died, and he will pass the rest of his long life producing official verse and revising the unpublished “Prelude” and, for the most part, making it worse. Nearly all readers prefer the version of 1805 to that of 1850.

Plumly tells us about all these matters as he discusses the nature of friendship; explicates Samuel Taylor Coleridge’s poem to Lamb, “This Lime-Tree Bower My Prison”; and reflects on Haydon’s passion for the Elgin Marbles and how their example inspires Keats: “These Greek classical models will prove, existentially, that poetry can be an act of transparency to the forces behind it, beauty naked in the presence of truth, though, first there must be truth.”

As that rather abstract sentence suggests, Plumly requires his reader to slow down and think hard, just as he himself has done. His is a poet’s prose, given to dithyramb, and it can’t be hurried along. Still, now and again, Plumly offers up a weary-hearted or shrewdly aphoristic observation: “Who knows where the acquired little daily defeats that at last overwhelm us come from?” “Drink, in good company, adds depth.” “A diary tends to be proved upon the pulses; an autobiography tends, ultimately, to justify.”

Throughout, Plumly probes artistic failure as well as success. In “Christ’s Entry into Jerusalem,” Haydon never quite gets Jesus’s face right — it lacks humanity and individuality (though it finally ends up slightly resembling the artist himself). Basically, Haydon tries too hard to achieve the sublime. In contrast, the living faces of Keats and Wordsworth, depicted in the crowd around Jesus, carry conviction. To modern eyes, Haydon’s sketches and the work he quickly dashes off always seem more vital than those to which he devotes years of effort. For some reason though, “The Immortal Evening” fails to provide any illustrations, apart from a frontispiece of “Christ’s Entry into Jerusalem.”

As one would expect from the author of the award­winning “Posthumous Keats,” Plumly quotes thrillingly from that poet’s letters (“the excellence of every Art is its intensity”) as well as his poems, and no less so from Wordsworth’s “Prelude,” Haydon’s intimate writings and Lamb’s essays. Here, for instance, is a portion of Lamb’s reflections on “New Year’s Eve”: “Sun, and sky, and breeze, and solitary walks, and Summer holidays, and the greenness of fields, and the delicious juices of meats and fishes, and society, and the cheerful glass, and candlelight and fireside conversations, and innocent vanities, and jests, and irony itself — do these things go out with life?”

As it happens, Plumly also transcribes part of a Haydon letter written on Dec. 31: “The last day of 1821. I don’t know how it is, but I grow less reflective as I get older. I seem to take things as they come without much care. In early life, everything being new excites thought. As nothing is new when a man is 35, one thinks less.” On another occasion, Haydon writes of his painting, “I leave off weary and commence in disgust!” Anyone who works in the arts knows that feeling all too well.

The “immortal dinner,” Stanley Plumly reminds us, was never about food or wine; it was always about “fellow-feeling.” Plumly, who teaches at the University of Maryland, dedicates this book to four fellow writers (and his wife), making clear how much they have all meant to him. In “The Immortal Evening,” then, he isn’t simply examining an iconic evening in 1817; he’s also reflecting on his own life, his own art, his own mortality.

THE IMMORTAL EVENING

A Legendary Dinner with Keats, Wordsworth, and Lamb

By Stanley Plumly

Norton. 368 pp. $26.95