"I suppose you have read in the papers of the mysterious burning of our country house at Oceanhurst, on the south shore of Long Island?"

It had been about the middle of the afternoon that a huge automobile of the latest design drew up at Kennedy's laboratory and a stylishly dressed woman, accompanied by a very attentive young man, alighted.

They had entered and the man, with a deep bow, presented two cards bearing the names of the Count and Countess Alessandro Rovigno.

Julia Rovigno, I knew, was the daughter of Roger Gaskell, the retired banker. She had recently married Count Rovigno, a young foreigner whose family had large shipping interests in America and at Trieste in the Adriatic.

"Yes, indeed, I have read about it," nodded Craig.

"You see," she hurried on a little nervously, "it was a wedding present to us from my father."

"Giulia," put in the young man quickly, giving her name an accent that was not, however, quite Italian, "thinks the fire was started by an incendiary."

Rovigno was a tall, rather boyish-looking man of thirty-two or thirty-three, with light brown hair, light brown beard and mustache. His eyes and forehead spoke of intelligence, but I had never heard that he cared much about practical business affairs. In fact, to American society Rovigno was known chiefly as one of the most daring of motor-boat enthusiasts.

"It may have been the work of an incendiary," he continued thoughtfully, "or it may not. I don't know. But there has been an epidemic of fires among the large houses out on Long Island lately."

I nodded to Kennedy, for I had myself compiled a list for the Star, which showed that considerably over a million dollars' worth of show places had been destroyed.

"At any rate," added the Countess, "we are burned out, and are staying in town now—at my father's house. I wish you would come around there. Perhaps father can help you. He knows all about the country out that way, for his own place isn't a quarter of a mile away."

"I shall be glad to drop around, if I can be of any assistance," agreed Kennedy as the young couple left us.

The Rovignos had scarcely gone when a woman appeared at the laboratory door. She was well dressed, pretty, but looked pale and haggard.

"My name is Mrs. Bettina Petzka," she began, singling out Kennedy. "You do not know me, but my husband, Nikola, was one of the first students you taught, Professor."

"Yes, yes, I recall him very well," replied Craig. "He was a brilliant student, too—very promising. What can I do for you?"

"Why, Professor Kennedy," she cried, no longer able to control her feelings, "he has suddenly disappeared."

"What line of work had he taken up?" asked Craig, interested.

"He was a wireless operator—had been employed on a liner that runs to the Adriatic from New York. But he was out of work. Someone has told me that he thought he saw Nikola in Hoboken around the docks where a number of the liners that go to blockaded ports are laid up waiting the end of the war."

She paused.

"I see," remarked Kennedy, pursing up his lips thoughtfully. "Your husband was not a reservist of any of the countries at war, was he?"

"No—he was first of all a scientist. I don't think he had any interest in the war—at least he never talked much about it."

"I know," persisted Craig, "but had he taken out his naturalization papers here?"

"He had applied for them."

"When did he disappear?"

"I haven't seen him for two nights," she sobbed.

It flashed over me that it was now two nights since the fire that had burned Rovigno's house, although there was no reason for connecting the events, at least yet.

The young woman was plainly wild with anxiety. "Oh, can't you help me find Nikola?" she pleaded.

"I'll try my best," reassured Kennedy, taking down on a card her address and bowing her out.

It was late in the afternoon before we had an opportunity to call at the Gaskell town house where the Rovignos were staying. The Count was not at home, but the Countess welcomed us and led us directly into a large library.

"I'd like to have you meet my father," she introduced. "Father, this is Professor Kennedy, whom Alex and I have engaged to look into the burning of our house."

Old Roger Gaskell received us, I thought, with a curious mixture of restraint and eagerness.

"I hope you'll excuse me?" asked the Countess a moment later. "I really must dress for dinner. But I think I've told you all I can. I wanted you to talk to my father."

"I've heard of the epidemic of fires from my friend Mr. Jameson here, on the Star," remarked Kennedy when we were alone. "Some, I understand, have attributed the fires to incendiaries, others have said they were the work of disgruntled servants, others of an architect or contractor who hasn't shared in the work and thinks he may later. I've even heard it said that an insurance man may be responsible—hoping to get new business, you know."

Gaskell looked at us keenly. Then he rose and approached us, raising his finger as though cautioning silence.

"Do you know," he whispered so faintly that it was almost lost, "sometimes I think there is a plot against me?"

"Against you?" whispered back Kennedy. "Why, what do you mean?"

"I can't tell you—here," he replied. "But, I believe there are detectaphones hidden about this house!"

"Have you searched?" asked Kennedy keenly.

"Yes, but I've found nothing. I've gone over all the furniture and such things. Still, they might be inside the walls, mightn't they?"

Kennedy nodded.

"Could you discover them if they were?" asked Gaskell.

"I think I could," replied Craig confidently.

"Then there's another peculiar thing," resumed Gaskell, a little more freely, yet still whispering. "I suppose you know that I have a country estate not far from my daughter?"

He paused. "Of course I know," he went on, watching Kennedy's face, "that sparks are sometimes struck by horses' shoes when they hit stones. But the shoes of my horses, for instance, out there lately have been giving forth sparks even in the stable. My groom called my attention to it, and I saw it myself."

He continued looking searchingly at Kennedy. "You are a scientist," he said at length. "Can you tell me why?"

Kennedy was thinking deeply. "I can't, offhand," he replied frankly. "But I should like to have a chance to investigate."

"There may be some connection with the fire," hinted Gaskell anxiously as he accompanied us to the door.

At our own apartment, when we returned, we found our friend, Burke, of the Secret Service, waiting for us.

"Just had a hurry call to come to New York," he explained, "and thought I'd like to drop in on you first."

"What's the trouble?" asked Kennedy.

"Why, there's been a mysterious yacht lurking about the mouth of the harbor for several days and they want to look into it."

"Whose yacht do they think it is?"

"They don't know, but it is said to resemble one that belongs to a man named Gaskell."

"Gaskell?" repeated Craig, turning suddenly.

"Yes,—the Furious—a fast, floating palace—one of these new power yachts, run by a gas engine—built for speed. Why, do you know anything about it?"

Kennedy said nothing.

"The revenue cutter Uncas has been assigned to me," went on Burke. "If you have nothing better to do, I'd like to have you give me a hand in the case. You might find it a little different from the ordinary run."

"I shall be glad to go with you," replied Craig cordially. "Only, just now I've got a particular case of my own. I'll see you tomorrow at the Customs House, though, if I can."

"Good!" exclaimed Burke. "I don't think either of you, particularly Jameson, will regret it. It promises to be a good story."

Burke had scarcely left us when Kennedy decided on his next move. We went directly over to the Long Island Railroad station and caught the next train out to Oceanhurst, not a long run from the city.

Thus, early in the evening, Kennedy was able to begin, under cover, his investigation of the neighborhood of the Rovigno and Gaskell houses.

We entered the Gaskell estate and looked it over as we made our way toward the stable to find the groom. Out on the bay we could see the Furious at anchor. Nearer in shore were a couple of Count Rovigno's speedy racing motor-boats. Along the shore, we saw a basin for yachts, capable even of holding the Furious.

The groom proved to be a rather dull-witted fellow, and left us pretty much to our own devices.

"Ya-as—sparks—I saw 'em," he drawled in answer to Kennedy's question. "So did Mr. Gaskell. Naw—I don't know nawthin' about 'em."

He had lumbered out into another part of the stable when I heard a low exclamation from Craig, of "Look, Walter!"

I did look in amazement. There were indeed little sparks, in fact a small burst of them in all directions, where there were metal surfaces in close proximity to one another.

Kennedy had brought along with him a strange instrument and he was now looking attentively at it.

"What is that?" I asked.

"The bolometer," he replied, "invented by Professor Langley."

"And what does it do?"

"Detects waves," he replied, "rays that are invisible to the eye. For instance, just now it tells me that shooting through the darkness are invisible waves, perhaps infra-red rays."

He paused, and I looked at him inquiringly.

"You know," he explained, "the infra-red rays are closer to the heat rays than those of the upper end of the spectrum and beyond, the ultra-violet rays, with which we have already had some experience."

Kennedy continued to look at his bolometer. "Yes," he remarked thoughtfully, half to himself, "somewhere around here there is a generator of infra-red rays and a projector of those rays. It reminds me of those so-called F-rays of Ulivi—or at least of a very powerful wireless."

I was startled at the speculations that his words conjured up in my mind. Was the "evil eye" of superstition a scientific fact? Was there a baneful beam that could be directed at will—one that could not be seen or felt until it worked its havoc? Was there a power that steel walls could not hold, which, in fact, was the more surely transmitted by them?

Somehow, the fact of the strange disappearance of Petzka, the wireless operator, kept bobbing up in my mind. I could not help wondering whether, perhaps, he had found this strange power and was using it for some nefarious purpose. Could it have been Petzka who was responsible for the fires? But, why? I could not figure it out.

Early the next morning we called at the Gaskell town house again. Kennedy had brought with him a small piece of apparatus which seemed to consist of two sets of coils placed on ends of a magnet bar. To them was attached a long flexible wire which he screwed into an electric light bulb socket. Then he placed a peculiar telephone-like apparatus, attached to the other end, to his ears. He adjusted the magnets and carried the thing carefully about the room.

At one point he stopped and moved the thing vertically up along the wall, from floor to ceiling.

"That's a gas pipe," he said simply.

"What's the instrument?" I asked.

"A new apparatus for finding pipes electrically, which I think can be just as well applied to finding other things concealed in walls under plaster and paper."

He paused to adjust the thing. "The electrical method," he went on, "is a special application of well-known induction balance principles. You see one set of coils receives an alternating or vibrating current. The other is connected with this telephone. First I established a balance so that there was no sound in the telephone."

He moved the thing about. "Now, when the device comes near metal-piping, for example, or a wire, the balance is disturbed and I hear a sound. That was the gas pipe. It is easy to find its exact location. Hulloa—"

He paused again in a corner, back of Gaskell's desk and appeared to be listening intently.

A moment later he was ruthlessly breaking through the plaster of the beautifully decorated wall.

Sure enough, in there was a detectaphone, concealed only a fraction of an inch beneath the paper, with wires leading down inside the partition in the direction of the cellar.