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.