The Earl and Countess of Donmount, while riding in Worcestershire, become enamoured of a peasant boy called Henry. After they discover from his putative father, Stephen, that his parentage is unknown, they offer to adopt him. Henry grows up to be an accomplished young man, but he feels compelled to leave, despite the protestations of the Earl, after Charles (the biological son of the Earl and Countess) repeatedly ridicules him on account of his humble origins.
Henry joins the army and, as a result of valiant conduct in Egypt, is promoted to the position of captain. While in Egypt a man appears to recognise him and faints, inexplicably. Upon returning to Worcestershire Henry rescues Virginia, the daughter of the Earl and Countess, whom he knew only as a small child, from a careering horse. Shortly after, he is reconciled to the Donmounts, including even Charles, who has grown up to be a ridiculous but inoffensive gentleman of fashion.
Henry goes to Cheltenham with Donmounts and falls in love with Virginia. During his excursion he attracts the attention of the Duke of Belvoir, who appears to resent him. After attending a masque, he is attacked by two men dressed as dominos, but manages to fend them off with the aid of the strange fainting man from Egypt who has mysteriously reappeared.
The Earl informs Henry that the Duke of Belvoir seeks to marry Virginia. Fortunately, the Duke is mortally wounded after attempting to seduce another Duke's wife. Visiting Belvoir on his deathbed, Henry learns that the Duke is his uncle. The servant (who, it is revealed, was the fainting man in Egypt) informs Henry that his father was the previous Duke. The uncle, seeking the title for himself, ordered the servant to murder the infant Henry. The servant, however, bungled the deed, then repented when he discovered that Henry was still alive, and deposited him secretly with a peasant couple. His parentage successfully established, Henry promptly marries Virginia.
Much of the second part of the novel satirises the customs and fashions of fashionable Cheltenham society. One particularly unusual scene occurs in volume three, when Henry and his friend William Caustic attend a masque. Caustic, in the costume of 'the satirist' issues withering remarks to the other guests, including a 'scotch woman' in the costume of Minerva.

Some West Country features (non-standard 'be') as well as grammatical features ('as' a a relative pronoun) and discourse markers ('Anan!') of unknown provenance (Anan!, as for that). The novel also includes some metalanguage about Stephen's odd similes and his tendency to take Henry's metaphorical utterances literally.
A brief sentence of Scots dialect occurs in volume 3 when a 'scotch woman' in the costume of Minerva appears. Sir William Caustic tells her not to 'bray'.
In addition to the dialectal content of 'Autumn at Cheltenham', the novel also features much of the cant of Charles and his fellow aristocratic gentlemen of fashion.

Unexpectedly nondialectal characters: Stephen, Henry's first adoptive father, speaks Standard English when he first appears, but later uses dialect.