Left alone, I again went over this unexpected letter. Reflection inclined me yet more strongly to believe that it was the work of a practical joker. My adventure was well known. The newspapers had given it in full detail. Some satirist, such as exists even in America, must have written this threatening letter to mock me. To assume, on the other hand, that the Eyrie really served as the refuge of a band of criminals, seemed absurd. If they feared that the police would discover their retreat, surely they would not have been so foolish as thus to force attention upon themselves. Their chief security would lie in keeping their presence there unknown. They must have realized that such a challenge from them would only arouse the police to renewed activity. Dynamite or melinite would soon open an entrance to their fortress. Moreover, how could these men have, themselves, gained entrance into the Eyrie unless there existed a passage which we had failed to discover? Assuredly the letter came from a jester or a madman; and I need not worry over it, nor even consider it. Hence, though for an instant I had thought of showing this letter to Mr. Ward, I decided not to do so. Surely he would attach no importance to it. However, I did not destroy it, but locked it in my desk for safe keeping. If more letters came of the same kind, and with the same initials, I would attach as little weight to them as to this. Several days passed quietly. There was nothing to lead me to expect that I should soon quit Washington; though in my line of duty one is never certain of the morrow. At any moment I might be sent speeding from Oregon to Florida, from Maine to Texas. And this unpleasant thought haunted me frequently if my next mission were no more successful than that to the Great Eyrie, I might as well give up and hand in my resignation from the force. Of the mysterious chauffeur or chauffeurs, nothing more was heard. I knew that our own government agents, as well as foreign ones, were keeping keen watch over all the roads and rivers, all the lakes and the coasts of America. Of course, the size of the country made any close supervision impossible; but these twin inventors had not before chosen secluded and unfrequented spots in which to appear. The main highway of Wisconsin on a great race day, the harbor of Boston, incessantly crossed by thousands of boats, these were hardly what would be called hiding-places! If the daring driver had not perished of which there was always strong probability; then he must have left America. Perhaps he was in the waters of the Old World, or else resting in some retreat known only to himself, and in that case— “Ah!” I repeated to myself, many times, “for such a retreat, as secret as inaccessible, this fantastic personage could not find one better than the Great Eyrie!” But, of course, a boat could not get there, any more than an automobile. Only high-flying birds of prey, eagles or condors, could find refuge there.