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,” replied Madame Doisty, “near the Esplanade des Invalides.” Lecoq had refrained from any sign of satisfaction while he was in the jeweler’s presence. But directly he had left the shop he evinced such delirious joy that the passers-by asked themselves in amazement if he were not mad. He did not walk, but fairly danced over the stones, gesticulating in the most ridiculous fashion as he addressed this triumphant monologue to the empty air: “At last,” said he, “this affair emerges from the mystery that has enshrouded it. At last I reach the veritable actors in the drama, the exalted personages whose existence I had suspected. Ah! Gevrol, my illustrious General! you talked about a Russian princess, but you will be obliged to content yourself with a simple marchioness.” But the vertigo that had seized the young detective gradually disappeared. His good sense reasserted itself, and, looking calmly at the situation, he felt that he should need all his presence of mind, penetration, and sagacity to bring the expedition to a successful finish. What course should he pursue, on entering the marchioness’s presence, in order to draw from her a full confession and to obtain full particulars of the murder, as well as the murderer’s name! “It will be best to threaten her, to frighten her into confession,” he soliloquized. “If I give her time for reflection, I shall learn nothing.” He paused in his cogitations, for he had reached the residence of the Marchioness d’Arlange--a charming mansion with a courtyard in front and garden in the rear. Before entering, he deemed it advisable to obtain some information concerning the inmates.