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.