Peacock researched his story from early Welsh materials, many of them untranslated at the time; he included many loose translations from bardic poetry, as well as original poems such as "The War-Song of Dinas Vawr".

Elphin has been highly praised for its sustained comic irony, and by some critics is considered the finest Arthurian literary work of the Romantic period.

One of Seithenyn's officials, Teithrin ap Tathral, discovers that the embankment is in a poor state of repair, and tells Elphin, son of king Gwythno.

Elphin then meets Angharad, Seithenyn's beautiful daughter, and together they watch the onset of a mighty tempest, which destroys the embankment so that the sea breaks through.

Seithenyn, with drunken bravado, leaps into the waves, sword in hand, but Teithrin, Elphin and Angharad make their escape to king Gwythno's castle.

On his way there he stops at Dinas Vawr, a fortress just captured by king Melvas, whose men are celebrating their victory in wine and song; among them he is astounded to find Angharad's father, Seithenyn ap Seithyn, who it turns out survived the flooding of Gwaelod so many years before.

It is possible that it had a long gestation because of the many other demands on Peacock's time, such as a full-time job at East India House and the work involved in serving as his friend Shelley's executor, and because his research was so assiduous, but it has also been argued that he did not begin to write it until late in 1827.

The narrative structure of Elphin is based on three ancient tales: the inundation of Gwythno's kingdom through the negligence of Seithenyn, the birth and prophecies of Taliesin, and the abduction of Gwenyvar by Melvas.

[19][20][4][21] Peacock also makes numerous ironic comments about the blessings of progress, and in his portrayal of the "plump, succulent" abbey of Avallon he attacks the over-comfortable clergy of the Church of England.

[20] Other targets of his satire include industrialization, the doctrine of utilitarianism, realpolitik, pollution, paper money, false literary taste and the Poet Laureateship.

Arthur is less than distraught at his wife's absence, Gwenyvar is no better than she ought to be, Merlin is a secret pagan whose supposed magic is merely natural philosophy, and such human frailties are seen as driving history.

[26] The appeal of The Misfortunes of Elphin for the modern reader depends largely its unusual blending of an Olympian irony with simple good humour.

B. Priestley analysed the stylistic devices which help to produce this effect: A crisp rhythm, a perfectly grave manner, a slight heightening of language, a curious little "smack" in each sentence, suggesting a faint and curiously droll over-emphasis in pronunciation if we think of the prose being spoken...the very restraint of the voice, its even tones, only serve to heighten the effect of the bland sarcasm and the lurking drollery that find their way into almost every sentence.

[27][30] He is "a Welsh Silenus, a tutelary spirit of an amiable and approachable type",[31] whose conversational style, with its alcoholically twisted logic, has led to his being repeatedly compared to Falstaff.

[46] Bryan Burns thought that "as a piece of story-telling which mingles celebration with attack, a subdued but trenchant treatment of themes of authority and individual freedom and an admirable achievement of style, it is hard to equal in the rest of Peacock's oeuvre.

[35] Peacock studied his early Welsh sources with respect for their vigour, sense of wonder, hyperbole and inventiveness with language, and is said by favourable critics to have evoked their spirit vividly while tempering them with "Attic lucidity and grace".

Bryan Burns wrote of "the insouciance and diversity of its story-telling ... there is real command in the spacing and contrasting of episodes, the organising of space and the economy and poise of individual scenes",[53] while Marilyn Butler judged that of all Peacock's books Elphin has the strongest plot,[54] but Priestley on the contrary believed that "he has no sense of narration, of the steady march forward of events, of the way in which action can be ordered to produce the best effect".

[56] There is wide agreement that the original poems in Elphin are superior to the translations and imitations, and that "The War-Song of Dinas Vawr", later taken up and adapted by T. H. White in The Once and Future King, is the best of them.