This is C. Auguste Dupin, my good friend and amazing puzzle solver. He's talking to a police man: a friend of his. A letter has been stolen detailing an affair. The culprit is known; they just don't know where the letter is. This man believes Dupin can find it because he is good at solving mysteries. Dupin simply tells him to research the house.
It's one month later, and the policeman is back. He says he'll give 50,000 francs to whoever can give him the letter. Dupin pulls out his wallet, hands it to the policeman, and after acquiring the money, gives him the letter.
Puzzled, I ask him how he got the letter. Dupin responds that the person who stole it is not too stupid to try and hide the letter, as the police force will most likely find it eventually. They're good at finding hidden areas.
Thus, he must have hidden the letter in plain sight. Upon searching the apartment, Dupin sees a letter hanging with some cards on the mantel. The letter, although disguised by the culprit, is the one that he stole.
Dupin has someone cause a commotion outside, then sneaks in, grabs the letter, and sneaks out. He replaces the letter with a fake.
The end! Sorry they make you sue either 3 or 6 panels that's it.