“But how? Whether genuine or not, the document is of no use to you if you do not manage to decipher it, because Louis XVI. destroyed the book that gave the explanation.” “Yes, but the other copy, which King Louis XVI.’s captain of the guards snatched from the flames, was not destroyed.” “How do you know?” “Prove the contrary.” After uttering this defiance, Beautrelet was silent for a time and then, slowly, with his eyes closed, as though trying to fix and sum up his thoughts, he said: “Possessing the secret, the captain of the guards begins by revealing it bit by bit in the journal found by his descendant. Then comes silence. The answer to the riddle is withheld. Why? Because the temptation to make use of the secret creeps over him little by little and he gives way to it. A proof? His murder. A further proof? The magnificent jewel found upon him, which he must undoubtedly have taken from some royal treasure the hiding-place of which, unknown to all, would just constitute the mystery of the Hollow Needle. Lupin conveyed as much to me; Lupin was not lying.” “Then what conclusion do you draw, Beautrelet?” “I draw this conclusion, my friends, that it be a good thing to advertise this story as much as possible, so that people may know, through all the papers, that we are looking for a book entitled _The Treatise of the Needle_. It may be fished out from the back shelves of some provincial library.” The paragraph was drawn up forthwith; and Beautrelet set to work at once, without even waiting for it to produce a result. A first scent suggested itself: the murder was committed near Gaillon. He went there that same day. Certainly, he did not hope to reconstruct a crime perpetrated two hundred years ago. But, all the same, there are crimes that leave traces in the memories, in the traditions of a countryside. They are recorded in the local chronicles. One day, some provincial archaeologist, some lover of old legends, some student of the minor incidents of the life of the past makes them the subject of an article in a newspaper or of a communication to the academy of his departmental town. Beautrelet saw three or four of these archaeologists. With one of them in particular, an old notary, he examined the prison records, the ledgers of the old bailiwicks and the parish registers. There was no entry referring to the murder of a captain of the guards in the seventeenth century. He refused to be discouraged and continued his search in Paris, where the magistrate’s examination might have taken place. His efforts came to nothing.