country. He has many agents, and is a man of great power."

"But why don't you arrest him?"

"Alas, mademoiselle, you do not understand. This Dr. Hartmann is a physician of great prominence. His cures of nervous and mental disorders have made him famous throughout Europe. He has in Brussels—just outside the city, a sanatorium, where he receives and treats his patients. He is looked up to by all. His work as an enemy of France is quite secret, known to but a few. Even we know very little about it."

"Then how do you know that he had anything to do with the matter of this snuff box?"

"We do not know it—we only surmise. There is a reason, which I am not permitted at present to tell you, which causes Monsieur Lefevre to believe that Dr. Hartmann had a hand in this matter. It is for that reason, indeed, that he has sent you here."

"What can I do?"

"I will tell you. For a long time we have tried to get one of our own agents into Dr. Hartmann's house, but without success. He is very shrewd—very cautious. All his servants are countrymen of his, upon whom he knows he can depend. His patients are people of wealth, position, standing, who, he knows, could not possibly be agents of the French police. He will take no others, and always insists upon the strictest references. It is for these reasons that we have failed. Now an opportunity presents itself for you, mademoiselle, to accomplish that which the police cannot accomplish. You are an American girl, of prominent family, of wealth, of position. I am informed that your aunt, by her second marriage, was the Countess d'Este. Should you apply to Dr. Hartmann for treatment, you will have no difficulty in obtaining admission, for he could not, by any chance, think that Miss Grace Ellicott, of New York, was in the employ of the French secret police. You observe, mademoiselle, Monsieur the Prefect's object in sending you to Brussels?"

Grace nodded. She was beginning to feel a keen interest in the matter. "But I am not ill," she said, with a laugh. "How can I ask Dr. Hartmann to treat me?"

"We have thought of that. The matter has been under consideration ever since we were advised, early this afternoon, that you were coming. We have thought it best that you represent yourself to the doctor as a somnambulist."

"A sleep walker?"

"Precisely. It is a form of nervous trouble which is by no means infrequent. We are informed that Dr. Hartmann has treated several such cases in the past. There are not symptoms, except a state of nervousness on the part of the patient which in your case it is probable the excitement of the enterprise will supply, and, of course, the tendency to walking in the sleep. This latter you must assume."

"Assume?"

"Yes. You must pretend to be a somnambulist. You must get up, each night, at some hour, and wander about the house—pretending to be oblivious of all about you. You are not normally conscious. You are in a walking dream. Your eyes are fixed ahead—seeing no one. It will not be difficult for you to pretend all this—and naturally, by wandering about in this way, you may—we hope you will—have excellent opportunities to observe what goes on within the doctor's walls."

"Is that all I am to do—just watch?"

"I think not. If we are unable, by other means, to prevent the stolen box from being delivered to Dr. Hartmann, it must be recovered from him, at any cost—at any cost whatever—" the woman repeated, significantly. "Even life itself cannot be spared, in this case. The box must be recovered, no matter what the price we pay—so we are informed by Monsieur Lefevre."

"Then if it should pass into his possession, I may have to steal it? Is that what you mean?"

"Undoubtedly, and at the very first opportunity." The girl rose, gathered up the soiled towels which she had taken from the bedroom, and went toward the door. "That is all, mademoiselle, except that you will communicate to us any news of importance by means of a young man who goes to the house each morning and evening to deliver bread. He comes in a small wagon, and you will no doubt be able to speak with him, as he enters or leaves the grounds. He is quite safe, and can be trusted. Address your communications to him verbally—no letters, understand; they are always dangerous. And now, let me suggest that you arrange to see Dr. Hartmann at once."

"But—he may require reference—credentials."

"We have thought of that, and have prepared the way. One of our men has ascertained that the United States Minister here is acquainted with you—that your family is known to him. Your aunt, you will remember, was quite prominent in society, in New York, at the time she married Monsieur the Count d'Este. Whether the Minister is acquainted with you personally, we have not been able to learn, but that he knows who you are, is certain."

"Then I had best call upon him, and arrange for letters to Dr. Hartmann."

"That is the best course. His house is near by. Take a cab at once, go to him, and state your errand. You will have no difficulty, I feel sure." She noiselessly opened the door, and in a moment was gone, leaving Grace in a state of wonder. She did not waste much time, however, in speculating upon the curious affair in which she found herself involved, but putting on her hat, started off at once in search of the American Minister.

CHAPTER III

When Richard Duvall and his companion entered the house of the French Ambassador in London, it was evident that their arrival was expected. The detective had no more than given his name to the butler who threw open the door, when the latter, with a bow of recognition, conducted them to a small reception-room to the right of the entrance, and informed them that Monsieur de Grissac would see them at once.

They did not have long to wait. The Ambassador, a thin, spare, nervous-looking man of sixty, with white hair and a gray-white mustache, came hurriedly into the room after but a few moments had elapsed, and greeting them excitedly, bade them be seated. He himself remained standing, his back to the fireplace, twirling his eyeglasses at the end of their black silk ribbon, and observing his visitors keenly.

"Monsieur Lefevre had informed me of your coming, gentlemen," he presently burst out. "We have no time to lose."

"Let us have the details of the affair, monsieur," Duvall remarked, seating himself comfortably in his chair. "So far we are completely in the dark."

"You know, do you not, that a valuable article, a small snuff box, to be exact—has been stolen from me?"

"Yes. Of that I have been informed," the detective remarked, dryly. "I am curious to learn why the loss of an article of so trivial a nature should be regarded with such seriousness."

The Ambassador's eyes snapped—he seemed almost to resent the detective's attitude. "It should be sufficient, monsieur, I think, that it is so regarded. The task before us is to recover it—not discuss the reasons for doing so."

"I disagree with you, monsieur. If the real value of the stolen article is kept from me, how can I draw any conclusions as to the probable object of its theft? Was it intrinsically valuable? Did it contain anything of value? In short, why should any one have taken the trouble to steal it? Tell me that, and I can act intelligently. Otherwise, I shall be only groping about in the dark."

"I do not think so, monsieur." The Ambassador bent upon Duvall a searching glance. "The fact that the box is gone should be sufficient. All that I ask is that you recover it. You must trace its disappearance from the material facts of the case. Conjecture will avail us nothing."

"Is the box then of no value?"

"I have not said so. As a matter of fact, its value is great. It has been an heirloom in my family for many years. At one time it belonged to Cardinal Mazarin."

"You think, then, that its intrinsic value alone might have prompted the