In the story, Dupin is consulted by the Prefect of Police who is searching desperately for a sensitive letter being used to blackmail a royal personage. The identity of the criminal is known, and circumstances indicate the letter is hidden in his residence, and yet a meticulous search has failed to produce it. In the end, it is Dupin who deduces its clever hiding place using his peculiar analytic ability.
"The Purloined Letter" has influenced numerous detective stories, including several Sherlock Holmes short stories. The story has been adapted for television as an episode of Suspense (1952), as "The Case of The Purloined Letter" (1979) with main characters recast in an episode of the Sherlock Holmes and Doctor Watson series, and as "The Pawloined Paper" (1988) for the children's series Wishbone with a canine title character.
The unnamed narrator and his friend C. Auguste Dupin are enjoying a quiet evening when they are visited by the Prefect of Police. The Prefect wishes to consult Dupin about a puzzling case involving a sensitive letter stolen from the royal apartments.
While perusing the letter, the royal personage was interrupted by the exalted personage from whom she wished to keep it a secret. She was forced to place the compromising letter on a table with just the address showing. Minister D—, entering the boudoir on business, saw the letter and, recognizing the handwriting and seeing her confusion, realized her secret. True to his daring nature, he put down his own letter on the table and, knowing she would not call attention to it, picked up her letter in its place. He has since used his power over her to political advantage.
Knowing that the minister must, due to political circumstances, keep the letter close at hand, the police have made a thorough search of his hotel during his frequent absences. They have scrutinized every room and every piece of furniture, probing cushions with needles, removing table tops to check legs for cavities, and even examining joints with a microscope. They have also searched the grounds and adjoining houses. The minister himself has been waylaid and searched twice. Dupin comments that the minister, not being a fool, must have anticipated the searches, but the Prefect replies that the minister is a poet and therefore only one step removed from a fool. Dupin asks for the description of the letter then recommends another thorough search. The Prefect leaves in low spirits.
A month later, the Prefect returns. The reward has now been doubled, and he is so desperate as to offer fifty thousand francs himself for the letter. Producing a checkbook, Dupin promises to hand him the letter once the check is signed. The Prefect stares incredulously at Dupin for some minutes before signing the check. Dupin unlocks the writing desk and takes out a letter. The Prefect gasps, glances at its contents, then scrambles out the door without a word.
Afterwards, Dupin explains the case to the narrator. Having confidence in the abilities of the police, he knew the fault lay not in the methods but the range of the search. Considering only their own ideas of ingenuity, they searched where they would have hidden the letter. The Prefect, believing all poets to be fools, underestimated the minister. Dupin, however, knew him also to be a mathematician. While a mathematician would not have confounded the police, the minister, being both a poet and a mathematician, would have reasoned better and known that the most intricate recesses would be open to the police. Being also bold and daring, he would have deliberately chosen simplicity, putting the letter under their nose rather than attempting to conceal it.
Expecting to find the letter in plain sight, Dupin called on the minister. While maintaining an animated discussion, he surveyed the apartment and spotted a card rack holding several visiting cards and a single letter. The crumpled letter, addressed in a female hand to the minister, was radically different in appearance from the Prefect's description. Its soiled condition was also inconsistent with the methodical habits of the minister. Convinced it was the stolen letter refolded inside out, Dupin memorized its appearance and, leaving a snuff box behind as an excuse to return, took his leave. Visiting again the following day, he substituted a facsimile he had prepared while the minister was distracted by a disturbance outside caused by a man in his pay.
Asked by the narrator why he replaced the letter instead of simply seizing it, Dupin explains that, not only did he want to get out alive, but he also meant to cause the minister's downfall. Ignorant of the loss, he would press the victim as usual only to have the table turned on him. Dupin then adds that he would like to know the minister's thoughts when, forced to open the letter, he finds the message he left inside just so the minister would know who outwitted him.