f such a valuable
jewel," he soliloquized, referring to the diamond earring. "And when
I find the owner I shall at the same time discover our mysterious
prisoner's identity."

The first step to be taken was to ascertain whom the earring had been
bought from. It would naturally be a tedious process to go from jeweler
to jeweler and ask: "Do you know this jewel, was it set by you, and if
so whom did you sell it to?" But fortunately Lecoq was acquainted with
a man whose knowledge of the trade might at once throw light on the
matter. This individual was an old Hollander, named Van Numen, who as a
connoisseur in precious stones, was probably without his rival in Paris.
He was employed by the Prefecture of Police as an expert in all such
matters. He was considered rich. Despite his shabby appearance, he was
rightly considered rich, and, in point of fact, he was indeed far more
wealthy than people generally supposed. Diamonds were his especial
passion, and he always had several in his pocket, in a little box which
he would pull out and open at least a dozen times an hour, just as a
snuff-taker continually produces his snuffbox.

This worthy man greeted Lecoq very affably. He put on his glasses,
examined the jewel with a grimace of satisfaction, and, in the tone of
an oracle, remarked: "That stone is worth eight thousand francs, and it
was set by Doisty, in the Rue de la Paix."

Twenty minutes later Lecoq entered this well-known jeweler's
establishment. Van Numen had not been mistaken. Doisty immediately
recognized the earring, which had, indeed, come from his shop. But whom
had he sold it to? He could not recollect, for it had passed out of his
hands three or four years before.

"Wait a moment though," said he, "I will just ask my wife, who has a
wonderful memory."

Madame Doisty truly deserved this eulogium. A single glance at the jewel
enabled her to say that she had seen this earring before, and that the
pair had been purchased from them by the Marchioness d'Arlange.

"You must recollect," she added, turning to her husband, "that the
Marchioness only gave us nine thousand francs on account, and that we
had all the trouble in the world to make her pay the balance."

Her husband did remember this circumstance; and in recording his
recollection, he exchanged a significant glance with his wife.

"Now," said the detective, "I should like to have this marchioness's
address."

"She lives in the Faubourg St. Germain," re