In Section 1, Twain gives the reader a tantalizing taste of some old Hadleyburg drama that unfolded an undisclosed amount of time before the story begins: Edward Richards reveals to his wife, Mary, that he could have saved the town's reverend, Burgess, from some unnamed disgrace but chose not to for fear of the town turning on him.
Mary struggles to balance her instinct for honesty against her gratitude for her husband's dishonesty—after all, it saved their reputation—and Twain uses metaphorical language to convey how this tension roils inside her:
"I—I don’t think it would have done for you to—to— One mustn’t—er—public opinion—one has to be so careful—so—” It was a difficult road, and she got mired; but after a little she got started again. “It was a great pity, but—Why we couldn’t afford it, Edward—we couldn’t indeed. Oh, I wouldn’t have had you do it for anything!"
By this metaphor, Mary's trial of navigating between her honesty and her conceit transforms into an actual rural road leading through difficult country. Her verbal stopping and starting becomes the jerking motions of a cart or wagon "mired" in a particularly muddy patch of road—but she manages to pull through, declaring at last that Edward made the right choice to protect himself despite the damage it did to Burgess.
This is a turning point in the story: it is the first instance the reader has of a Hadleyburg citizen's honesty crumbling before their vanity. As the story progresses, of course, this will become a regular feature of the plot: as soon as the citizens learn of the mysterious sack of gold, they begin to bend themselves backward to appear honest and just about finding the treasure's rightful owner—even as they begin to privately scheme to claim it for themselves.
In "The Man That Corrupted Hadleyburg," Twain presents honesty as the primary virtue of Hadleyburg's citizens. As the story progresses, a motif emerges that presents this honesty in terms of the contrast between its strength as the town's reputation and its fragility as an actual trait in its citizens. This motif is established through a number of metaphors, the first of which occurs in the opening paragraph of Section 1:
Also, throughout the formative years temptations were kept out of the way of the young people, so that their honesty could have every chance to harden and solidify and become a part of their very bone.
In this passage, Twain treats honesty as a metaphorical component of the very bones of the Hadleyburg citizens—a strong, defining trait, but liable to effect the citizens to their very core when it is threatened or revealed to be weak.
This weakness is made gradually apparent throughout the rest of the story. Later in Section 1, when Mary Richards reveals her thoughts on the town to her husband, Edward, she uses the metaphorical language of a petrified and rotten substance (such as bone or fossil):
God knows I never had shade nor shadow of a doubt of my petrified and indestructible honesty until now—and now, under this very first big and real temptation, I—Edward, it is my belief that this town’s honesty is as rotten as mine is; as rotten as yours is.
While Twain paints this “petrified” or calcified honesty as a great strength in the beginning of the story, a strength that has grown over time like a bone, Mary's speech emphasizes instead its incredible, inevitable fragility.
The Hadleyburg citizens' honesty is supposedly the source of their virtue, but, as Mary suggests, the citizens' pride in their honesty is little more than proof of their extreme vanity—a vanity that will be an existential risk to the town.
There are two treasures in "The Man That Corrupted Hadleyburg": one literal (the sack of gold that the stranger leaves in town) and one metaphorical (the unassailable virtue of honesty in Hadleyburg's nineteen prominent citizens that turns out, by the end of the story, to be quite assailable indeed). The tension between these two treasures presents a central irony of the story: despite being in possession of one treasure, Hadleyburg's Nineteen fall over themselves to seize the other—which turns out to be fake.
In Reverend Burgess's speech to the crowd in Section 3, before he unwittingly reveals every one of the Nineteen save Edward Richards to be a fraud, Twain plays on this metaphorical characterization of the town's honesty as treasure:
And who is to be the guardian of this noble treasure—the community as a whole? No! The responsibility is the individual, not communal. From this day forth each and every one of you is in his own person its special guardian, and individually responsible that no harm shall come to it.
The irony of the situation only increases, as Twain adds dramatic irony into the mix: Burgess has just emphasized the singular importance of individual integrity to safeguard the town's reputation by pronouncing the citizens the "guardians" of this honor, and yet the reader is well aware that each and every one of the Nineteen are about to betray it in the hopes of inheriting the gold.
Later, in the stranger’s postscript to the citizens, he emphasizes the impossible wealth of virtue that has been lost:
You had an old and lofty reputation for honesty, and naturally you were proud of it—it was your treasure of treasures, the very apple of your eye.
The gold turns out to be lead—the promised treasure is worthless—and the honesty that Hadleyburg's Nineteen sacrificed in vain turns out to be the only thing valuable that was actually at stake. They recklessly "exchanged" their virtue for the prospect of material wealth—and, in the process, revealed their extreme vanity.
