The dull, heavy sleep into which Richard Duvall had fallen, after Dr. Hartmann had left him, was suddenly disturbed by the realization that someone had seized him roughly by the arms. He attempted to rise, struggling instinctively against the two men who, he dimly saw, were bending over him, but his resistance was useless. In a moment the leather straps which encircled his wrists and ankles had been drawn tight, and he felt himself being lifted bodily and deposited on the floor in the center of the room. At first he cried out, cursing his captors loudly, but an instant's reflection showed him how profitless his remonstrances were, and he allowed himself to be bound to the floor in silence. In a moment, Dr. Hartmann—the detective saw that it was he, with Mayer—had switched on the violet light, and he once more felt its blinding radiance upon his face.

Hartmann opened the door. "I shall be back again in a few hours," he said, as he left the room. "I hope that by that time you will have quite recovered your senses."

The detective made no reply. He had definitely made up his mind upon one point: he was not going to purchase his freedom at the expense of his duty. The unfortunate situation in which he now found himself was, he knew very well, entirely his own fault, and his desire to atone for his momentary carelessness made him determined not to accede to Dr. Hartmann's demands. He hoped that his friends outside—Lablanche, Dufrenne, even Grace—might be able to come to his assistance. If he could only know that the snuff box was safe in Monsieur Lefevre's hands, the rest did not matter much.

These thoughts passed through his mind as he lay with closed eyes, his face quivering under the dazzling light which fell upon it. Its intensity was, he thought, greater, if anything, than it had been before, and the irritating effect upon his eyes more pronounced. He did not open his eyes at all, on this occasion, for fear even a momentary exposure would increase their sensitiveness.

Slowly the day passed. He concluded that it was afternoon, when he heard far off a bell striking the hour of two, although it might equally well have been two o'clock in the morning, for all he could tell. There was a faint hum of conversation in the laboratory above him, which convinced him that it was still day.

Presently his ear, acutely sensitive to the slightest noise which might disturb the stillness about him, became aware of a faint sound of music, which seemed to come to him from a long distance off. It was a popular French march, and from a certain quality of the notes he concluded that it was being played upon a phonograph. The strains of the music distracted him, took his mind from the things about him, and as he listened to it, it seemed that the effort of keeping his eyes tightly closed grew sensibly less, the blinding pressure of the unwavering light cone upon his face appreciably easier to bear. He knew that this was but a momentary relief, but he welcomed it eagerly. Lying in this terrifying silence, under the cruel glare of light, had become frightful—he wondered if, after all, his nerves, his mind, could long stand the strain.

The music stopped suddenly. He found himself eagerly hoping that there would be more. In a few moments it began again, and he was listening to the familiar strains of The Rosary. He had always liked the song—Grace, too, had been fond of it. He wondered if she could be playing to him, trying to soothe his fast-shattering nerves with music. It pleased him to think that it might be so, although he had no reason to suppose that Grace knew of the torture to which Dr. Hartmann was subjecting him.

After a time, the final strains of The Rosary died away, to be followed by a German march, played by some military band. This, too, he was glad to hear, although he found himself thinking that he preferred The Rosary. As if in answer to his thoughts, it began again—he found himself repeating the words to himself mechanically, and thinking of Grace.

The music continued for long over an hour. Duvall noted with surprise that while there were many other selections, The Rosary was played almost every other time. So often, in fact, did its strains break the stillness, that he became annoyed—in his nervous state this constant repetition of the song worried him. After a time he shuddered when he heard it, hoping that each time would be the last. No one but an imbecile, he muttered to himself, could enjoy playing a piece over and over in that aimless fashion. When at last the impromptu concert had ceased, and the silence about him was once more unbroken, he found himself puzzling in vain over the matter, as though it had become of vast importance to him.

After the music ceased, he realized how much it had helped him to endure the two or more hours which had elapsed since Hartmann left him. His real tortures were only just beginning. The constant blaze of light on his face, the ceaseless effort to keep his eyes closed, to turn his head away, in spite of the bonds which prevented it, once more almost frenzied him. He fell to wondering whether Hartmann had been in earnest, when he told him of the qualities of the violet rays. Could they in any way affect his mind? The mere thought stimulated his imagination to such an extent that already he was convinced that his senses were wandering—that his mind was becoming sluggish and dull.

As hour after hour passed, this thought became almost a certainty. His head began again to ache terribly, his eyes seemed to swim in pools of liquid fire. Bright flashes of light darted through his brain, and at times it seemed almost on fire. The pain which the constant effort to turn his head caused, was becoming more acute as each minute passed—he felt constantly on the point of screaming out in terror—begging for release—agreeing to do anything they asked of him. Then with a mighty effort of the will he would calm himself, and closing his eyes tightly once more, determine to endure until the end.

After an interminable period, the sound of the music once more fell upon his troubled brain. This time the strains sounded more distinct and clear. Three times in rapid succession The Rosary was played, then sudden silence. He waited in vain for more—dreading the recurrence of the song, yet expecting it, as one expects the continuance of any oft-repeated sound. There was nothing further, however, and once more the silence became like the darkness about him, a grim and positive thing.

Hours later, when his brain reeled endlessly in a blazing redness, and his tortured eyes seemed bursting from their sockets, the cone of violet light vanished as though some silent hand had brushed it aside, and in the reaction he fainted.

He awoke again to find himself lying on the floor, with Hartmann bending over him, feeling his pulse. In a fit of rage, he struck out with his clenched hand, and missing, scrambled to his feet. The room was faintly lit by the single electric globe, and he saw Mayer and Dr. Hartmann confronting him, the latter with a revolver in his hand. Once more he realized the futility of resistance, and sank against a packing box, his hand covering his burning eyes.

The latter appeared to be no longer in his former state of sardonic good nature. "Are you ready to tell us what you have done with the box?" he snarled.

Duvall made no reply, and this angered the doctor still further. "I'll give you an hour to think the matter over," he said, furiously. "And if you don't come to terms by that time, you shall stay under the influence of the light until you do." He turned toward the door, followed by Mayer, and in a moment they had left the room.

Duvall, in his pain and distress, realized that something would have to be done at once, within the next hour, in fact, or he would be obliged to give up. Physical torture he could stand, but to lie here silently, under that cruel radiance, and realize that his brain was slowly giving way, he felt he could not endure.

Yet what was there that he could do? The walls of the room, of solid brick, he could not hope to penetrate. The door, of iron, a dozen men could not break through. He forced his shoulder against it, and laughed bitterly as he realized that with all his strength he could not even cause it to give the fraction of an inch. He determined to get the snuff box—to examine it—reckless of his fear of being observed. In a moment he had snatched the opera hat from the corner, torn out the lining, and held the box in his hand.

He paused for a moment, listening intently. Everything about him was still. There were no sounds from the laboratory above. He remembered now that he had not heard Hartmann and his companion ascend the iron stairway. Doubtless they had returned to the main building by means of the lower corridor.

In a moment he had hung the torn opera hat over the knob of the door, to prevent anyone from observing him through the keyhole, and going directly beneath the bracket which held the electric globe, proceeded to examine the box carefully.

The first thought that came to his mind, filled him with a strange feeling of hope. He had no more than glanced at the top of the box when he saw what he had previously failed to observe, that the circle of pearls upon its top formed a rosary, which was completed by the ivory cross in the center. The Rosary! Why had this song been so persistently and continuously played? Was it for him, some message, indeed, intended to show him a way out of his difficulties? Yet if so, to what did it lead? There was a rosary upon the top of the box, it is true, but what of it? Absently he began to count the pearls, hardly realizing what he was doing. One of them, he noted, the one at the very top of the cross, was larger than the others, and he started here, slowly counting around the circumference of the box. His eyes pained him frightfully and twice he lost count and had to begin all over again, but on the third attempt he discovered that the pearls numbered twenty-six. Even yet, the significance of this fact did not occur to him—he began to count the pearls again, mechanically.

Then suddenly, in a flash, the thing came to him. Twenty-six pearls—twenty-six letters in the alphabet. Evidently the box, in some way, formed a cipher, a secret alphabet, which might be used in correspondence, or in the preparation of important documents, yet how—how?

With repressed eagerness he held the box more closely to the light, searching its surface for some further clue. At once he noticed the arrangement of the concentric circles of letters which made up the Latin prayer. The words were so written that each letter stood opposite a pearl, and reading inward from each pearl, there was a row of letters six deep reaching almost to the center of the box. Clearly here were six different ciphers, that is, six circles of twenty-six letters each, any one of which might constitute a working cipher. It was only necessary to call the big pearl at the top "A," and here were six different letters opposite it, any one of which, in a system of cipher writing, might be used as the letter A.

Duvall, however, knew enough about ciphers to know that such an arrangement constituted no cipher at all, in other words, that ciphers so simple, so readily solved, as this, would never be employed in any case where absolute secrecy was imperative. He felt that there was something more to the matter than he had so far discovered.

Suddenly he saw that, just beyond each pearl, was engraved on the ivory rim of the box a number—starting with the large pearl at the top as number one, the circle of numbers ran around the edge of the box until it returned to its starting point, at number twenty-six. In his efforts to see these numbers, which were very small, he gripped the box tightly in his hands to hold it the more steadily toward the rather dim light. In doing so, he suddenly became aware of the fact that the rim or edge of the box, containing the numbers and the circle of pearls, was movable. It fitted so cunningly into the top of the box, that the joint appeared not as a crack or perceptible space, but merely as a fine thin line, apparently a part of the engraving on its surface. Holding the lower part of the box firmly in his left hand, he turned the rim of the top slowly about. At once the purpose of this became apparent. Not only had each pearl, representing a letter of the alphabet, six corresponding values from rim to center, in any one position, but by turning the rim around, twenty-six such positions could be secured, making a total of one hundred and fifty-six different alphabets from which a person desiring to use a cipher might choose.

Again, however, Duvall was conscious of a feeling of disappointment. One hundred and fifty-six different ciphers were no better than a single one, if only one were used. Evidently he had not yet reached the solution of the problem. In employing such a system of ciphers, some combination, precisely similar to the combinations used on the locks of safes, would have to be used. It was absolutely necessary, in order to insure safety, to use not one cipher, but a large number, changing the arrangement of the letters with each line written—even with each word, in order to defy solution. Yet such an arrangement being purely arbitrary, could not well be trusted to memory, for, once forgotten, the translation of the document written, even by the writer himself, would be absolutely impossible. It occurred to him that as there were six different concentric lines of lettering, each constituting in itself a complete cipher, the obvious way to use the box would be to place the pearls in a given position, write six words, using a different alphabet for each word, and then shift the ring of pearls to a new position, and repeat the operation. This, of course, could be done indefinitely, although half a dozen changes would be sufficient to insure a cipher that would absolutely defy solution. Where, however, was the key? That, after all, was the important matter; without it, the snuff box would be as useless to Monsieur de Grissac as it would be to his enemies themselves.

For many minutes Duvall puzzled over the matter, unable to reach any satisfactory conclusion. Then he began to think of the song which had so clearly been repeated, over and over, as a message to him from outside. The words of the refrain began to run aimlessly through his mind, his eyes upon the box. Suddenly he realized that the word cross, in its repetitions, its position as the final word of the song, must have a definite meaning. Before his eyes he saw the cross, so delicately carved as to project scarcely an eighth of an inch above the thin and fragile ivory surface. Instinctively he began to push at it, pressing it this way and that, to discover, if possible, any spring or other means whereby it might be made to turn or lift up. As he did so, his fingers unconsciously pressed upon the large pearl at the top. In a moment the upper surface of the cross slid to one side, disclosing a tiny shallow cavity beneath it, some quarter of an inch in either direction, and no deeper than the thickness of a piece of cardboard. Within this lay a bit of tissue paper, tightly folded.

Duvall drew it carefully out and examined it. Upon it were written six numbers: 12-16-2-8-20-4. There was nothing else upon the paper, but Duvall realized that he held in his hand the key of the cipher.

At once Monsieur de Grissac's agitation, the servant NoËl's death, Hartmann's persecution of him, became clear. Evidently there were documents, somewhere, of some nature, which this cipher made intelligible and which, without it, were proof against all attempts to read them. What were these documents? Were they in Hartmann's hands? These questions, he knew, could not be answered now.

Immediately the question rose in his mind: What should he do next? By destroying the tiny slip of paper, he could render the snuff box valueless. Without the key, no one could use it with success. But, the key once destroyed, how could Monsieur de Grissac himself read the documents, for the preparing of which it had been utilized? Possibly, if Hartmann had such documents, they were but copies, obtained through the corruption of some clerk, while the originals remained in De Grissac's possession. For these reasons he dared not destroy the cipher, at least until all other means of escape had been exhausted. Then he realized, in a flash, that if he proposed to utilize the return of the snuff box as a means of obtaining his freedom, he could not hope to do so, if the key was removed. Doubtless Hartmann knew of its existence. In some way he had learned, possibly through the murdered man NoËl, that the box contained such a key, and would examine it, and satisfy himself that it had not been removed, before he would allow him to leave the place. This would inevitably result in his being searched, and the key, concealed about his person, found. He stood in an agony of doubt, wondering which alternative he should take.

His reflections were rudely disturbed by the sound of footsteps in the corridor outside the door. In a moment he had replaced the tiny bit of paper in the recess beneath the cross, slid the latter back into place, and thrust the box beneath a mass of straw which lay on top of the packing case against which he had been leaning. Then he turned toward the door and had barely time to hurl the opera hat into a dark corner, when the door opened, and Hartmann appeared on the threshold.