The story begins in the home office of private investigator C. Auguste Dupin, while he and his friend, an unnamed narrator, entertain the Prefect of the Paris Police, Monsieur G. The Prefect has come to Dupin again in need of help. Monsieur G has a case which he cannot solve, involving a purloined (stolen) letter. Without hesitation, Dupin is able to tell the Prefect exactly where the letter is, solely based on the description of the case.
According to the Prefect, a young lady (it is implied she is royalty) was in possession of a letter which contained damaging information. As she read it in her suite, an “exalted personage” from whom she wished to hide the letter, and a certain “Minister D”, entered the room. While the letter almost went unnoticed, Minister D saw it and discerned that it contained damning information. The minister switched the letter with a similar one of no consequence, and has since been blackmailing her.
At the direction of this powerful lady, Monsieur G has repeatedly searched every inch of the Minister’s house and office, with no results. Without hesitation Dupin tells the Prefect that the letter is indeed still in the minister's apartment. With a large reward at stake for its return, the Prefect leaves Dupin to go search again. After a month the Prefect returns to Dupin’s and says he cannot find the letter. At which point Dupin produces the letter and explains how he retrieved it.
Knowing the minister, Dupin placed himself in the minister's shoes. He knew that he would keep it close to him and that he was intelligent to know where the police would look for it. Therefore, he hid it in plain sight, slightly disguised as a letter of his own. Dupin then went to speak with the minister, purposely leaving behind his tobacco box, so that he could return. When he did, he had arranged a commotion outside the minister’s window at the same time, so that he could swipe the letter and replace it with another, much like the minister did.