I confess that at first this letter dumfounded me. “Ohs!” and “Ahs!” slipped from my open mouth. The old servant stared at me, not knowing what to think.

“Oh, sir! is it bad news?”

I answered for I kept few secrets from this faithful soul by reading her the letter from end to end. She listened with much anxiety.

“A joke, without doubt,” said I, shrugging my shoulders.

“Well,” returned my superstitious handmaid, “if it isn’t from the devil, it’s from the devil’s country, anyway.”

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.

The nineteenth of June I was going to the police bureau, when, on leaving my house, I noticed two men who looked at me with a certain keenness. Not knowing them, I took no notice; and if my attention was drawn to the matter, it was because my servant spoke of it when I returned.

For some days, she said, she had noticed that two men seemed to be spying upon me in the street. They stood constantly, perhaps a hundred steps from my house; and she suspected that they followed me each time I went up the street.

“You are sure?” I asked.

“Yes, sir, and no longer ago than yesterday, when you came into the house, these men came slipping along in your footsteps, and then went away as soon as the door was shut behind you.”

“You must be mistaken!”

“I am not, sir.”

“And if you met these two men, you would know them?”

“I would.”

“Good;” I cried, laughing, “I see you have the very spirit for a detective. I must engage you as a member of our force.”

“Joke if you like, sir. But I have still two good eyes, and I don’t need spectacles to recognize people. Someone is spying on you, that’s certain; and you should put some of your men to track them in turn.”

“All right; I promise to do so,” I said, to satisfy her. “And when my men get after them, we shall soon know what these mysterious fellows want of me.”

In truth I did not take the good soul’s excited announcement very seriously. I added, however, “When I go out, I will watch the people around me with great care.”

“That will be best, sir.”

My poor old housekeeper was always frightening herself at nothing. “If I see them again,” she added, “I will warn you before you set foot out of doors.”

“Agreed!” And I broke off the conversation, knowing well that if I allowed her to run on, she would end by being sure that Beelzebub himself and one of his chief attendants were at my heels.

The two following days, there was certainly no one spying on me, either at my exits or entrances. So I concluded my old servant had made much of nothing, as usual. But on the morning of the twenty-second of June, after rushing upstairs as rapidly as her age would permit, the devoted old soul burst into my room and in a half whisper gasped “Sir! Sir!”

“What is it?”

“They are there!”

“Who?” I queried, my mind on anything but the web she had been spinning about me.

“The two spies!”

“Ah, those wonderful spies!”

“Themselves! In the street! Right in front of our windows! Watching the house, waiting for you to go out.”

I went to the window and raising just an edge of the shade, so as not to give any warning, I saw two men on the pavement.

They were rather fine-looking men, broad-shouldered and vigorous, aged somewhat under forty, dressed in the ordinary fashion of the day, with slouched hats, heavy woolen suits, stout walking shoes and sticks in hand. Undoubtedly, they were staring persistently at my apparently unwatchful house. Then, having exchanged a few words, they strolled off a little way, and returned again.

“Are you sure these are the same men you saw before?”

“Yes, sir.”

Evidently, I could no longer dismiss her warning as a hallucination; and I promised myself to clear up the matter. As to following the men myself, I was presumably too well known to them. To address them directly would probably be of no use. But that very day, one of our best men should be put on watch, and if the spies returned on the morrow, they should be tracked in their turn, and watched until their identity was established.

At the moment, were they waiting to follow me to police headquarters? For it was there that I was bound, as usual. If they accompanied me I might be able to offer them a hospitality for which they would scarce thank me.

I took my hat; and while the housekeeper remained peeping from the window, I went down stairs, opened the door, and stepped into the street.

The two men were no longer there.

Despite all my watchfulness, that day I saw no more of them as I passed along the streets. From that time on, indeed, neither my old servant nor I saw them again before the house, nor did I encounter them elsewhere. Their appearance, however, was stamped upon my memory, I would not forget them.

Perhaps after all, admitting that I had been the object of their espionage, they had been mistaken in my identity. Having obtained a good look at me, they now followed me no more. So in the end, I came to regard this matter as of no more importance than the letter with the initials, M. o. W.

Then, on the twenty-fourth of June, there came a new event, to further stimulate both my interest and that of the general public in the previous mysteries of the automobile and the boat. The Washington Evening Star published the following account, which was next morning copied by every paper in the country.

“Lake Kirdall in Kansas, forty miles west of Topeka, is little known. It deserves wider knowledge, and doubtless will have it hereafter, for attention is now drawn to it in a very remarkable way.

“This lake, deep among the mountains, appears to have no outlet. What it loses by evaporation, it regains from the little neighboring streamlets and the heavy rains.

“Lake Kirdall covers about seventy-five square miles, and its level is but slightly below that of the heights which surround it. Shut in among the mountains, it can be reached only by narrow and rocky gorges. Several villages, however, have sprung up upon its banks. It is full of fish, and fishing-boats cover its waters.

“Lake Kirdall is in many places fifty feet deep close to shore. Sharp, pointed rocks form the edges of this huge basin. Its surges, roused by high winds, beat upon its banks with fury, and the houses near at hand are often deluged with spray as if with the downpour of a hurricane. The lake, already deep at the edge, becomes yet deeper toward the center, where in some places soundings show over three hundred feet of water.

“The fishing industry supports a population of several thousands, and there are several hundred fishing boats in addition to the dozen or so of little steamers which serve the traffic of the lake. Beyond the circle of the mountains lie the railroads which transport the products of the fishing industry throughout Kansas and the neighboring states.

“This account of Lake Kirdall is necessary for the understanding of the remarkable facts which we are about to report.”

And this is what the Evening Star then reported in its startling article. “For some time past, the fishermen have noticed a strange upheaval in the waters of the lake. Sometimes it rises as if a wave surged up from its depths. Even in perfectly calm weather, when there is no wind whatever, this upheaval sometimes arises in a mass of foam.

“Tossed about by violent waves and unaccountable currents, boats have been swept beyond all control. Sometimes they have been dashed one against another, and serious damage has resulted.

“This confusion of the waters evidently has its origin somewhere in the depths of the lake; and various explanations have been offered to account for it. At first, it was suggested that the trouble was due to seismic forces, to some volcanic action beneath the lake; but this hypothesis had to be rejected when it was recognized that the disturbance was not confined to one locality, but spread itself over the entire surface of the lake, either at one part or another, in the center or along the edges, traveling along almost in a regular line and in a way to exclude entirely all idea of earthquake or volcanic action.

“Another hypothesis suggested that it was a marine monster who thus upheaved the waters. But unless the beast had been born in the lake and had there grown to its gigantic proportions unsuspected, which was scarce possible, he must have come there from outside. Lake Kirdall, however, has no connection with any other waters. If this lake were situated near any of the oceans, there might be subterranean canals; but in the center of America, and at the height of some thousands of feet above sea-level, this is not possible. In short, here is another riddle not easy to solve, and it is much easier to point out the impossibility of false explanations, than to discover the true one.

“Is it possible that a submarine boat is being experimented with beneath the lake? Such boats are no longer impossible today. Some years ago, at Bridgeport, Connecticut, there was launched a boat, The Protector, which could go on the water, under the water, and also upon land. Built by an inventor named Lake, supplied with two motors, an electric one of seventy-five horse power, and a gasoline one of two hundred and fifty horse power, it was also provided with wheels a yard in diameter, which enabled it to roll over the roads, as well as swim the seas.

“But even then, granting that the turmoil of Lake Kirdall might be produced by a submarine, brought to a high degree of perfection, there remains as before the question how could it have reached Lake Kirdall? The lake, shut in on all sides by a circle of mountains, is no more accessible to a submarine than to a sea-monster.

“In whatever way this last puzzling question may be solved, the nature of this strange appearance can no longer be disputed since the twentieth of June. On that day, in the afternoon, the schooner ‘Markel’ while speeding with all sails set, came into violent collision with something just below the water level. There was no shoal nor rock near; for the lake in this part is eighty or ninety feet deep. The schooner with both her bow and her side badly broken, ran great danger of sinking. She managed, however, to reach the shore before her decks were completely submerged.

“When the ‘Markel’ had been pumped out and hauled up on shore, an examination showed that she had received a blow near the bow as if from a powerful ram.

“From this it seems evident that there is actually a submarine boat which darts about beneath the surface of Lake Kirdall with most remarkable rapidity.

“The thing is difficult to explain. Not only is there a question as to how did the submarine get there? But why is it there? Why does it never come to the surface? What reason has its owner for remaining unknown? Are other disasters to be expected from its reckless course?”

The article in the Evening Star closed with this truly striking suggestion: “After the mysterious automobile, came the mysterious boat. Now comes the mysterious submarine.

“Must we conclude that the three engines are due to the genius of the same inventor, and that the three vehicles are in truth but one?”