but the imaginings of a diseased mind—products of a delusion.

In every other respect the narrators had been, in appearance at least, perfectly sane individuals. While he hesitated to think that Oakes might have been suffering from an overworked brain at the time, still he knew that it was not impossible.

The struggles that the servants had heard had been those of Oakes; the actual evidences so far of assault were vague. Oakes was in a partially unconscious condition, to be sure; but what evidence of violence was that?

Moore's cool professional judgment told him that queer sensations are common after a severe shock, whether delusional in origin or not.

He had known Oakes for years, and the good judgment and coolness that he had always shown spoke greatly against a recently developed mental disorder.

Still, Moore was uneasy; he longed for more evidence of physical force from without—something more positive.

Of course, Oakes was not alone in his experience—there had been others—but it was possible that the mere contagion of terror might be in part responsible for some of these. There had been no witnesses. The statement of violence rested on the word of the victims alone. Dr. Moore knew that men thinking constantly of the same thing, to the exclusion of all else, might develop similar delusions. The physician had seen many strange things, and was not a man to be easily deceived. Could it be that Quintus Oakes was the victim of a mental process?

It was this very power which Moore possessed—of thinking along such lines—that made him, in Oakes's opinion, a particularly desirable addition to the party. Little, however, did the detective imagine that the trained mind of the physician would first weigh the possibilities of Oakes's own mental instability.

While Moore was deep in thought, he was suddenly interrupted by the bell, and the receipt of a note which had been delivered by the postman.

He glanced at the postmark, and saw that it was from Station O and was mailed at 4:30.

Somehow, he felt an instinctive dread of its contents. Of course, he as yet had no adequate cause for misgivings; but there was that in the subject of which he had been thinking that seemed to forecast evil and dread. His mind was in a state of unrest at the very thought of the possibilities. He tore the letter open, and read:

"Dear Dr. Moore: You may not deem it wise to pay attention to an anonymous communication, but let me assure you that, if you value a life, you will pay attention in this case.

"It has come within my province to know that a great tragedy may be averted by you.

"Some short while ago a man, tall, straight as an arrow, and with blue eyes, went to the town of Mona and stopped at the Mansion. There he came near being murdered, and if he ever goes back, I personally know that he will be killed in short order.

"His business was said to be that of an agent for the owners. I saw him in New York several years ago, and he was pointed out to me as a celebrated detective, but I cannot remember his name, or that of the person who informed me.

"At Mona he was known by another name. I cannot go there, however, or learn any more particulars. The reason I address this to you is that I know that you are acquainted with him, as years ago I used to see him often in your company.

"Now please communicate with this man; you are the only thread that I have to his identity.

"Reach him, if possible, at once. Warn him. Tell him to turn back—to abandon his quest, for death to him is the only alternative.

"Do not attempt to trace my identity. Act, and act quickly, if you wish to prevent a great horror."

The letter terminated abruptly. Dr. Moore realized in an instant that Oakes's movements were known to some outsider already—someone who had either been in Manhattan that day, or who had sent the letter there to one who had mailed it.

He saw the whole matter in a most serious light. Oakes was in danger from forces he did not suspect, perhaps, and the assault he had described had been known to others besides the immediate household of servants. For who, of that household, could have written such a letter?

Moore thought of his plans gone astray, of his business engagements, but they all paled into insignificance in the face of the danger to Oakes.

He decided to follow up Oakes by the very next train. Finding he had time for one or two calls, he rushed in his carriage to make them, and as he entered his office upon his return he found an energetic young man awaiting him. He knew him as Martin, one of Oakes's aides.

"Good evening, Doctor! You're on the rush tonight. My! but I had to hustle."

"Good evening! But how did you know so much of my movements—how, why, did you have to hustle?"

"I just arrived here a few seconds ago. I have been watching you this evening. Mr. Oakes told me to take care of you and keep you out of mischief. You see, he feared trouble of some kind. I was told to report to you once in a while—and here I am."

The physician understood, and then they discussed the recent development. It was agreed that Dr. Moore should leave for Mona; and this, after arranging his business by telephone and hastily making ready, he succeeded in doing.

As he boarded the train he asked of Martin, who was with him, if he was to go to Mona also.

"That depends upon who enters after you. If I think you are followed, I go too." And Moore realized that Oakes's hand of caution had been shown once more.

CHAPTER VI

The Murder

The rising sun was invisible from the little station hidden in the gloom of the hill, but away out on the river its rays reached the water and marked out sharply the shadow of the high ground.

Further down the stream the rugged outlines of the Mansion were cut in silhouette on the surface of the river, which was, as yet, smooth as a mill-pond, but which soon would be moved by those thousands of ripples advancing from the opposite shore.

As the sun shot his beams clearer and sharper, the mist of the distance unfolded and the rays struck the ragged granite cliffs of the shore, and revealed them yellow and gray in the bluish haze of the morn.

Away up, miles beyond, the river broadened and the mountains of both sides rose abruptly and ruggedly, apparently from the water's edge, causing the effect of a wide, placid lake.

All was quiet, lonely and dark on this side of the shore under the hill, but beyond, where the rays of the sun had reached, was beginning life and activity.

A schooner, becalmed until now, began to move with the breeze that greeted the waking of day.

The train had but just left the little station, and again had two strangers alighted. One, the older, trudged up the hill covered with a great-coat, and with hands in his pockets. He walked rather rapidly, looking sharply around once or twice. As he neared the top, where the country rolls off into the plain, he turned to admire the spectacle of the breaking day. His glance followed the road, and he saw below the second figure walking along in a hurry, as though to make up for lost time.

He smiled and said to himself: "That fellow Martin is a persistent youngster, anyway."

A few yards more brought him to the crest of the hill; then he suddenly stopped, for before him was unfolded a stretch of rolling