While Richard Duvall was thus flying toward Boulogne, racking his brains in a futile attempt to discover the reasons for his sudden and unexpected dispatch to London, Grace, his wife, equally mystified, was proceeding in the direction of Brussels.

The reasons for her going to Brussels were no more clear to her than were Richard's, to him. At the conclusion of the wedding breakfast which had followed her simple marriage to Duvall, she had gone to the pension at which she had been living, to await her husband's return. She had not then understood the mysterious message which had summoned him to the Prefect's office, nor, for that matter, had he, but he had assured her that he would return in a short while, and that had been enough for her.

Her patient waiting had been finally terminated by the arrival of the Prefect himself, who had explained with polite brevity that a matter of the gravest importance had made it necessary for him to send Richard at once to London.

The girl's grief and alarm had been great—Monsieur Lefevre had at last, however, succeeded in convincing her that Richard could not under the circumstances have done anything but go. His position as an assistant to Lefevre, and more particularly the friendship which existed between them, made it imperative for him to come to the Prefect's assistance in this crisis.

What the crisis was, Grace did not learn. She had insisted upon following Richard, upon being near him, upon assisting him, should opportunity offer, and Monsieur Lefevre, seized with a sudden inspiration, had dispatched her to Brussels, with the assurance that she would not only see her husband very soon, but might be able to render both him, and France, a very signal service.

Grace had accepted the mission; her desire to be near Richard was a compelling motive, and as a result she found herself flying toward the Belgian frontier, on an early afternoon express, with no idea whatever of what lay before her, and only a few words, written by Monsieur Lefevre upon a page torn from his notebook, to govern her future actions.

She luckily was able to find a compartment in one of the first-class carriages where she could be alone, and sank back upon the cushioned seat, determined to face whatever dangers the future might hold, for the sake of her husband.

Her mind traveled, in retrospect, over the events of the past few months—the conspiracy against her, by her step-uncle, Count d'Este, by which he had so nearly deprived her of the fortune left to her by her aunt, and the striking way in which his plans had been upset by Richard Duvall. She had loved him at their very first meeting, and now that they had become husband and wife, she loved him more than ever. It is small wonder that the thought of the way in which he had been suddenly torn from her, on the eve of their wedding journey, brought tears to her eyes.

Presently she regained her composure and looked at the sheet of paper which the Prefect had handed to her. It contained but a few words: "Proceed to the Hotel Metropole, Brussels. Take a room in the name of Grace Ellicott, and wait further instructions." That was all—no hint of how or when she and Richard were to meet, or what had been the cause of their separation. Once more the cruelty of the situation brought tears to her eyes. While feeling in her handbag for her handkerchief, she drew out the small silver ring which the Prefect had handed to her at the last moment. "Trust any one," he had said, "who comes to you with such a token as this." She examined the ring carefully, but the singular device worked in gold upon the silver band, meant nothing to her. At length she placed the ring carefully upon her finger, and proceeded to cover it by putting on her glove.

For a long time she sat, speculating upon the strange workings of fate, which doomed her to be thus speeding alone to Brussels, instead of to Cherbourg, en route to America, with Richard by her side. The sight of two lovers, who boarded the train at St. Quentin, increased her dissatisfaction. They came into the compartment, evidently quite wrapped up in each other, and even the presence of a third person did not prevent them from holding each other's hands under the cover of a friendly magazine, and gazing at each other with longing eyes. Grace was quite unable to endure the sight of their happiness—she turned away and buried herself in her thoughts.

Presently the adventure-loving side of her nature began to assert itself. Richard had been sent on a mission of the greatest importance—one involving, Monsieur Lefevre had told her, the honor of both his country and himself. And she was to share it—to take part in its excitement, its dangers. The thought stirred all her love of the mysterious, the unusual. After all, since she had become the wife of a man whose profession in life was the detection of crime, should she not herself take an interest, an active part in his work, and thereby encourage and assist him? The thought made her impatient of all delay—she felt herself almost trying to urge the train to quicker motion—she was glad when at last they roared into the station at Brussels.

Grace had never before been in the Belgian capital, but she summoned a cab, and proceeded without difficulty to the Hotel Metropole. Here she was assigned to a small suite, and at once began to unpack the steamer trunk which was the only baggage she had brought with her. It was after four o'clock when she had completed this task, and had removed the stains of travel and changed her gown. As she came into the tiny parlor which formed the second of the two rooms of the suite, she heard a tapping at the door, and upon opening it, discovered one of the hotel maids, waiting outside with fresh towels. The girl came in, and busied herself setting to rights the toilet articles on the washstand. Grace, who was engaged in listlessly watching the traffic in the square outside, paid no attention to her. Presently she heard the girl come in from the bedroom, and inquire if there was anything else that she could do for her. "Nothing," she replied, without turning. The maid, however, did not leave the room, but stood near by, observing her. Grace faced about. "That is all," she said sharply.

"I have something to say to you, mademoiselle," the girl whispered in a low tone, as she took a step forward. "A message from Monsieur Lefevre."

"Monsieur Lefevre? You?"

"Yes, mademoiselle, I am in his confidence. I know the purpose of your visit here, and I come to give you further instructions." She spoke quietly, impressively, and Grace was convinced that she was what she represented herself to be. Still, she felt the necessity of caution. "Please explain," she remarked, without further committing herself.

The girl approached still closer, and reaching into the bosom of her dress, drew out a ring similar to the one which the Prefect had given Grace. It was attached to a bit of ribbon. She glanced at the ring on Grace's finger and smiled. "May I suggest, mademoiselle," she said, "that you place the ring you are wearing where it will be less conspicuous?"

Grace colored slightly at the criticism which the woman's words implied, but drew the ring from her finger and placed it in her purse. "What have you to say to me?" she inquired.

"This, mademoiselle. Certain persons, whose identity is not known to the police, have committed a theft in London—in fact, have stolen a valuable article from the French Ambassador there, Monsieur de Grissac. This theft was committed this morning."

"What did they steal?" asked Grace.

"Monsieur de Grissac's ivory snuff box, mademoiselle."

"His snuff box? You don't mean to say that they are making all this fuss over a trifling thing like a snuff box?"

"Yes, mademoiselle. Such is, indeed, the case."

"But why?"

"That I cannot tell. I do not know. It is sufficient to me that Monsieur Lefevre wishes it recovered. In our service, mademoiselle, we are not supposed to ask questions, but to obey orders."

Grace repressed her annoyance as best she could. "I suppose it must be very valuable," she remarked, lamely.

"Undoubtedly. Very valuable, as you say. Now that it is stolen, it must be recovered without delay. Monsieur Lefevre informs us here in Brussels that others have gone to London to recover it. Should they fail to do so—we believe that the persons who have committed the theft will come here."

"Why?"

"Because they are acting, we believe, in the interests of a certain Dr. Hartmann, who is a resident of Brussels."

"Why should this Dr. Hartmann want the box?" asked Grace, somewhat mystified.

"That I am unable to tell you. He is an enemy of my 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.