In a small room in Paris, an unnamed narrator, who also narrates “The Murders in the Rue Morgue,” sits quietly with his friend, C. Auguste Dupin. He ponders the murders in the Rue Morgue, which Dupin solved in that story. Monsieur G——, the prefect of the Paris police, arrives, having decided to consult Dupin again. The prefect presents a case that is almost too simple: a letter has been taken from the royal apartments. The police know who has taken it: the Minister D——, an important government official. According to the prefect, a young lady possessed the letter, which contains information that could harm a powerful individual. When the young lady was first reading the letter, the man whom it concerned came into the royal apartments. Not wanting to arouse his suspicion, she put it down on a table next to her. The sinister Minister D—— then walked in and noted the letter’s contents. Quickly grasping the seriousness of the situation, he produced a letter of his own that resembled the important letter. He left his own letter next to the original one as he began to talk of Parisian affairs. Finally, as he prepared to leave the apartment, he purposely retrieved the lady’s letter in place of his own. Now, the prefect explains, the Minister D—— possesses a great deal of power over the lady.
Dupin asks whether the police have searched the Minister’s residence, arguing that since the power of the letter derives from its being readily available, it must be in his apartment. The prefect responds that they have searched the Minister’s residence but have not located the letter. He recounts the search procedure, during which the police systematically searched every inch of the hotel. In addition, the letter could not be hidden on the Minister’s body because the police have searched him as well. The prefect mentions that he is willing to search long and hard because the reward offered in the case is so generous. Upon Dupin’s request, the prefect reads him a physical description of the letter. Dupin suggests that the police search again.
One month later, Dupin and the narrator are again sitting together when the prefect visits. The prefect admits that he cannot find the letter, even though the reward has increased. The prefect says that he will pay 50,000 francs to anyone who obtains the letter for him. Dupin tells him to write a check for that amount on the spot. Upon receipt of the check, Dupin hands over the letter. The prefect rushes off to return it to its rightful owner, and Dupin explains how he obtained the letter.
Dupin admits that the police are skilled investigators according to their own principles. He explains this remark by describing a young boy playing “even and odd.” In this game, each player must guess whether the number of things (usually toys) held by another player is even or odd. If the guesser is right, he gets one of the toys. If he is wrong, he loses a toy of his own. The boy whom Dupin describes plays the game well because he bases his guesses on the knowledge of his opponent. When he faces difficulty, he imitates the facial expression of his opponent, as though to understand what he thinks and feels. With this knowledge, he often guesses correctly. Dupin argues that the Paris police do not use this strategy and therefore could not find the letter: the police think only to look for a letter in places where they themselves might hide it.
Dupin argues that the Minister D—— is intelligent enough not to hide the letter in the nooks and crannies of his apartment—exactly where the police first investigate. He describes to the narrator a game of puzzles in which one player finds a name on a map and tells the other player to find it as well. Amateurs, says Dupin, pick the names with the smallest letters. According to Dupin’s logic, the hardest names to find are actually those that stretch broadly across the map because they are so obvious.
With this game in mind, Dupin recounts the visit he made to the Minister’s apartment. After surveying the Minister’s residence, Dupin notices a group of visiting cards hanging from the mantelpiece. A letter accompanies them. It has a different exterior than that previously described by the prefect, but Dupin also observes that the letter appears to have been folded back on itself. He becomes sure that it is the stolen document. In order to create a reason for returning to the apartment, he purposely leaves behind his snuffbox. When he goes back the next morning to retrieve it, he also arranges for someone to make a commotion outside the window while he is in the apartment. When the Minister rushes to the window to investigate the noise, Dupin replaces the stolen letter with a fake. He justifies his decision to leave behind another letter by predicting that the Minister will embarrass himself when he acts in reliance upon the letter he falsely believes he still possesses. Dupin remarks that the Minister once wronged him in Vienna and that he has pledged not to forget the insult. Inside the fake letter, then, Dupin inscribes, a French poem that translates into English, “So baneful a scheme, if not worthy of Atreus, is worthy of Thyestes.”