Dupin

Let's look at E.A. Poe's [1809-1849] famous detective story with Dupin, the precursor to Sherlock Holmes and Arsène Lupin by Maurice Leblanc [1864-1941]. Read it all here. The story uses initials with dashes to make it seem like the author is referencing real people and families that he dare not wholly name.

Remember, Dupin leaves a note for the bad man, called only 'D' in the story, in his card rack near where Dupin had put the fake letter he created [to replace the one he stole]. The note says only:
"'— Un dessein si funeste, S'il n'est digne d'Atrée, est digne de Thyeste. They are to be found in Crebillon's 'Atrée.'"
A design [ie plan] so fatal, it's not the dignity of Atreus, it's the dignity of Thyestes.

This refers to a 1707 play by Académie Française seatholder Frenchman Prosper Jolyot (the sieur de Crébillon; 1674-1762). The play Atrée et Thyeste is about so named twin brothers from Mycenae in Greece who violently and ruthlessly vie with and hate each other. In a sense Dupin is mocking his enemy 'D' for not being smarter, since he was obviously quite bright in hiding something in plain sight. He gave the desired letter such a gross, dirty envelope that no one thought it was the right one, even though it was out in the open in plain sight. Dupin is saying he and his enemy 'D' are very alike, but he won in this instance. [*Don't confuse this Atreus with Myst island and the computer game.]

Here's an excerpt where Dupin describes where he found the letter a man was holding a noblewoman hostage with:

It [ie. the letter] was thrust carelessly, and even, as it seemed, contemptuously, into one of the uppermost divisions of the rack.

"No sooner had I glanced at this letter, than I concluded it to be that of which I was in search. To be sure, it was, to all appearance, radically different from the one of which the Prefect had read us so minute a description. Here the seal was large and black, with the D— cipher; there it was small and red, with the ducal arms of the S— family. Here, the address, to the Minister, diminutive and feminine; there the superscription, to a certain royal personage, was markedly bold and decided; the size alone formed a point of correspondence. But, then, the radicalness of these differences, which was excessive; the dirt; the soiled and torn condition of the paper, so inconsistent with the true methodical habits of D—, and so suggestive of a design to delude the beholder into an idea of the worthlessness of the document; these things, together with the hyper-obtrusive situation of this document, full in the view of every visiter, and thus exactly in accordance with the conclusions to which I had previously arrived; these things, I say, were strongly corroborative of suspicion, in one who came with the intention to suspect.

"I protracted my visit as long as possible, and, while I maintained a most animated discussion with the Minister upon a topic which I knew well had never failed to interest and excite him, I kept my attention really riveted upon the letter. In this examination, I committed to memory its external appearance and arrangement in the rack; and also fell, at length, upon a discovery which set at rest whatever trivial doubt I might have entertained. In scrutinizing the edges of the paper, I observed them to be more chafed than seemed necessary. They presented the broken appearance which is manifested when a stiff paper, having been once folded and pressed with a folder, is refolded in a reversed direction, in the same creases or edges which had formed the original fold. This discovery was sufficient. It was clear to me that the letter had been turned, as a glove, inside out, re-directed, and re-sealed. I bade the Minister good morning, and took my departure at once, leaving a gold snuff-box upon the table.

"The next morning I called for the snuff-box, when we resumed, quite eagerly, the conversation of the preceding day. While thus engaged, however, a loud report, as if of a pistol, was heard immediately beneath the windows of the hotel, and was succeeded by a series of fearful screams, and the shoutings of a terrified mob. D— rushed to a casement, threw it open, and looked out. In the meantime, I stepped to the card-rack, took the letter, put it in my pocket, and replaced it by a fac-simile, (so far as regards externals,) which I had carefully prepared at my lodgings—imitating the D— cipher, very readily, by means of a seal formed of bread.