There is a summary here: http://www.enotes.com/man-corrupted
but basically, An omniscient narrator opens the story with a description of Hadleyburg, U.S.A., as "honest," "upright," and very proud of its "unsmirched" reputation. The town enjoys national renown for protecting every citizen against all temptation from infancy through death. Appropriately, the town motto reads "Lead us not into temptation.'' The tale then segues to the bitter thoughts of an "offended stranger,’’ who has nursed a grudge against the town during the past year for an unnamed, unrequited offense. Rather than murder the one or two individuals responsible, the stranger plots vengeance to "comprehend the entire town, and not let so much as one person escape unhurt.’’ The ‘‘mysterious, big’’ stranger puts his scheme into action when he delivers a sack of gold coins, supposedly worth $40,000, to the home of Mary and Edward Richards, who is a cashier at the Hadleyburg bank. The man is repaying for a loan of 20 dollars from the town. They advertise to find the benefactor. The residents of Hadleyburg and curious visitors gather at the town hall to learn the identity of the sack's rightful owner. As instructed, Burgess presides over the meeting. At the urging of the crowd, Burgess opens the sack to retrieve the sealed envelope. Instead, he finds two envelopes, and one of them is labeled, "Not to be examined until all written communications which have been addressed to the Chair—if any—have been read.’’ Burgess opens the unmarked envelope, which contains a note that reads, ‘‘Go, and reform—or, mark my words—some day, for your sins, you will die and go to hell or Hadleyburg—TRY AND MAKE IT THE FORMER.’’ The note exposes the greed of the claimants and the hypocrisy of the town.
Burgess then opens the second envelope, which reveals the entirety of the stranger's scheme as well as a suggestion that the gold be used to establish a ‘‘Committee on Propagation and Preservation of the Hadleyburg Reputation.’’ The coins, however, are merely gilded slugs.
After receiving payment from Harkness, the stranger writes four checks in the amount of $1500 and one for $34,000, each payable to "Bearer." Keeping one of the smaller checks for himself, he delivers the rest to the Edward along with a note extolling their honesty, which proved that he failed to ‘‘corrupt the whole town.’’ Later, Edward receives a message from Burgess explaining that he refrained from naming him during the proceedings as a gesture of gratitude for Edward's advice to leave town before news of his scandal broke. Reminded of his cowardice and stung by guilt, Edward burns the checks.