He ripped the little mechanical eavesdropper out, wires and all, but he did not disconnect the wires, yet.

We traced it out, and down into the cellar the wires led, directly, and then across, through a small opening in the foundations into the next cellar of an apartment house, ending in a bin or storeroom.

In itself the thing, so far, gave no clew as to who was using it or the purpose for which it had been installed. But it was strange.

"Someone was evidently trying to get something from you, Mr. Gaskell," remarked Craig pointedly, after we returned to the Gaskell library. "Why do you suppose he went to all that trouble?"

Gaskell shrugged his shoulders and averted his eyes.

"I've heard of a yacht outside New York harbor," added Craig casually.

"A yacht?"

"Yes," he said nonchalantly, "the Furious."

Gaskell met Kennedy's eye and looked at him as though Craig had some occult power of divination. Then he moved over closer to us.

"Is that detectaphone thing out of business now?" he asked, hoarsely.

"Yes."

"Absolutely?"

"Absolutely."

Gaskell leaned over.

"Then I don't mind telling you, Professor Kennedy," he said in a low tone, "that I am letting a friend of mine from London use that yacht to supply some allied warships on the Atlantic with news, supplies and ammunition, such as can be carried."

Kennedy looked at him keenly, but for some moments did not answer. I knew he was debating on how he might properly dove-tail this with Burke's case, ethically.

"Someone is trying to find out from eavesdropping just what your plans are, then," remarked Craig thoughtfully, with a significant tap on the detectaphone.

A moment later he turned his back to us and knelt down. He seemed to be wrapping the detectaphone up in a small package which he put in his pocket and closing the hole in the wall as best he could where he had ripped the paper.

"All I ask of you," concluded Gaskell, as we left a few minutes later, "is to keep your hands off that phase of things. Find the incendiary—yes; but this other matter that you have forced out of me—well—hands off!"

On our way downtown to keep the appointment Kennedy had made with Burke the night before, he stopped at the laboratory to get a heavy parcel which he carried along.

We found Burke waiting for us, impatiently, at the Customs House.

"We've just discovered that the liners over at Hoboken have had steam up for a couple of days," he said excitedly. "Evidently they are waiting to make a break for the ocean—perhaps in concert with a sortie of the fleets over in Europe."

"H-m," mused Kennedy, looking fixedly at Burke, "that complicates matters, doesn't it? We must preserve American neutrality."

He thought a moment. "I should like to go aboard the revenue cutter. May I?"

"Surely," agreed Burke.

A few moments later we were on the Uncas, Kennedy and Burke in earnest conversation in low tones which I did not overhear. Evidently Craig was telling him just enough of what he had himself discovered so as to enlist Burke's services.

The captain in charge of the Uncas joined the conversation a few moments later, and then Kennedy took the heavy package down below. For some time he was at work in one of the forward tanks that was full of water, attaching the thing, whatever it was, in such a way that it seemed to form part of the skin of the ship.

Another brief talk with Burke and the captain followed, and then the three returned to the deck.

"Oh, by the way," remarked Burke, as he and Kennedy came back to me, "I forgot to tell you that I have had some of my men working on the case and one of them has just learned that a fellow named Petzka, one of the best wireless operators,—a Hungarian or something—has been engaged to go on that yacht."

"Petzka?" I repeated involuntarily.

"Yes," said Burke, in surprise, "do you know anything about him?"

I turned to Kennedy.

"Not much," replied Craig. "But you can find out about him, I think, through his wife. He used to be one of my students. Here's her address. She's very anxious to hear from him. I'm sure that if you have any news she will be only too glad to receive it."

Burke took the address and a little while later we went ashore.

I was not surprised when Kennedy proposed, as the next move, to revisit the cellar in the apartment next to Gaskell's house. But I was surprised at what he said, after we had reached the place.

All along I had supposed that he was planning to wait there in hope of catching the person who had installed the detectaphone. That, of course, was a possibility, still. But in reality he had another purpose, also.

We had scarcely secreted ourselves in the cellar storeroom, which was in a dark corner where one might remain unobserved even if the janitor entered the cellar, provided he did not search that part, when Kennedy took the receiving headpiece of the detectaphone and placed it over his head, quite as if nothing had happened.

"What's the use of that?" I queried. "You ripped the transmitter out up above."

He smiled quietly. "While my back was turned toward you, so that you couldn't see," he said, "I slipped the thing back again, only down further where Gaskell wouldn't be likely to find it, even if he looked. I don't know whether he was frank with us, so I thought I'd try the eavesdropping game myself, in place of the man who put this thing in in the first place, whoever he was."

We took turns listening, but could hear not a sound. Nor did anyone come into the cellar.

So a good part of the afternoon passed, apparently fruitless.

My patience was thoroughly exhausted when, suddenly, a motion from Craig revived my flagging interest. I waited impatiently for him to tell me what it was that he heard.

"What was it?" I asked finally as he pulled the receivers off his head and stood for a moment, considering.

"At first I heard the sound of voices," he answered quickly. "One was the voice of a woman, which I recognized. It was the Countess. The other was the Count.

"'Giulia,' I heard him say, as they entered the room, 'I don't see why you should want to go. It's dangerous. And besides, it's none of our business if your father lets his yacht be used for such a purpose.'

"'But I want to go, Alex,' she said. 'I will go. I'm a good sailor. It's father's yacht. He won't care.'

"'But what's the use?' he expostulated. 'Besides—think of the danger. If it was our business, it might be different.'

"'I should think you'd want to go.'

"'Not I. I can get all the excitement I want in a motor-boat race without risking my precious neck pulling the chestnuts out of the fire for someone else.'

"'Well, I want the adventure,' she persisted, petulantly.

"'But, Giulia, if you go tonight, think of the risk—'

"That was the last I heard as they left the room, still arguing. Evidently, someone is going to pull off something tonight."

It did not take Kennedy long to make up his mind what to do next. He left the cellar hurriedly and in the laboratory hastily fixed up a second heavy and bulky package similar to that which he had taken down to the revenue cutter earlier in the day, making it into two parcels so as to distribute the burden between us.

That night we journeyed out to Oceanhurst again. Avoiding the regular road, we made our way from the station to the Gaskell place by a roundabout path and it was quite dark by the time we got there.

As we approached the basin we saw that there were several men about. They appeared to be on guard, but since Oceanhurst at that season of the year was pretty deserted and the Gaskell estate was out of the town, they were not especially vigilant.

Dark and grim, with only one light showing weakly, lay the yacht, having been run into the basin, now. A hawser had been stretched across the mouth of the basin. Outside was a little tender, while a searchlight was playing over the water all the time. Evidently whatever interference was feared was expected from the water rather than from the land.

We slunk into the shadow of a row of bath-houses, in order to get our bearings. On the opposite side from the road that led down from the house, it was not so likely that anyone would suspect that interlopers were hiding there.

Still, they were not neglecting that side of the basin, at least in a perfunctory sort of way.

Kennedy drew me back into the shadow, deeper, at the sound of footsteps on the boardwalk leading in front of the bath-houses.

From our hiding place we could now hear two voices, apparently of sailors.

"Do you know the new wireless operator who goes with us tonight?" asked one.

"No. They've been very careful of him. I guess they were afraid that someone might get wise. But there couldn't very well be any leak, there. One of those Englishmen has been with him every minute since he was engaged."

"They say he's pretty good. Who is he?"

"A Servian, he says, and his name sounds as if it might be so."

The voices trailed off. It was only a scrap of conversation, but Kennedy had not missed a word of it.

"That means Petzka," he nodded to me.

"What is he—a Hungarian or a Servian?" I asked quickly.

Kennedy had craned his neck out beyond the corner of the bath-houses and was looking at the Furious in the basin.

"Come on, Walter," he whispered, not taking time to answer my question. "Those fellows have gone. There's no one at all on this side of the basin and I just saw the men on deck go up the gangplank to the boat-house. They can't do any more than put us off, anyhow."

He had watched his chance well. As quickly as we could, burdened down by our two heavy packages, we managed to slip across the boardwalk to the piling that formed that side of the basin. The Furious had swung over with the tide nearer our side than the other. It was a daring leap, but he made it as lightly as a cat, landing on the deck. I passed over the packages to him and followed.

Kennedy scarcely paused to glance about. He had chosen a moment when no one was looking, and, bending down under the weight of the packages we dodged back of a cabin. A dim light shining into the hold told us that no one was there and we dived down. It was the work of a moment to secrete ourselves in the blank darkness behind a pile of boxes, aft.

A noise startled us. Someone was coming down the steep, ladder-like stairs. A moment later we heard another noise. There were two of them, moving about among the boxes. From our hiding place we could overhear them talking in hoarse whispers, but could not see them.

"Where did you put them?" asked a voice.

"In every package of explosives and in as many of the boxes of canned goods as I had time. There wasn't much opportunity except while the stuff was in the boat-house."

I looked at Kennedy, wild-eyed. Was there treachery in the crew? He was leaning forward as much as our cramped quarters would permit, so as not to miss a word.

"All right," said the other voice. "No one suspects?"

"No. But the Secret Service has been pretty busy. They suspect something—but not this."

"Good. You are sure that you can detonate them when the time comes?"

"Positive. Everything is working fine. I've done my part of it. Changing wireless operators gave me just the chance I wanted."

"All right. I guess I'll go now."

"Remember the signal. As soon as the things are detonated I will get off, some way, by wireless the S O S—as if it came from the fleet, you understand?"

"Yes—that will be the signal for the dash. Good luck—I'm going ashore now."

As they passed up the ladder, I could no longer restrain myself.

"Craig," I cried, "this is devilish!"

I thought I saw it all now. In the cases of goods on the Furious were some terrible infernal machines which had been hidden, to be detonated by these deadly rays of wireless.

Kennedy was busy, working quickly putting together the parts he had taken from the two packages we had carried.

As I watched him, I realized that the burning of the Rovigno house was not the action of an incendiary, after all. It had been done by these deadly rays, probably by mere accident.

As nearly as I could make it out, there was a counterplot against the Furious. Somewhere was an infernal workshop, possibly hedged about by doors of steel which ordinary force would find hard to penetrate, but from which, any moment, this super-criminal might send out his deadly power.

The more I considered it, while Kennedy worked, the more uncanny it seemed. This man had rendered the mere possession of explosives more dangerous to the possessor than to the enemy.

Archimedes had been outdone!

The problem before us now was not only the preservation of American neutrality, but the actual safety of life.

Through the open hatch I could now hear voices on the deck. One was that of a woman, which I recognized quickly. It was Julia Rovigno.

"I'll be just as quiet as a mouse," she was saying. "I'll stay in the cabin—I won't be in the way."

I could not hear the man's voice in reply, but it did not sound like Rovigno's. It was rather like Gaskell's.

Still, we had heard enough to know that Julia Rovigno was on the yacht, had insisted on going on the expedition for the excitement of the thing, just as we had heard over the detectaphone.

"Hadn't we better warn her?" I asked Craig, who had paused in his work at the sound of voices.

Before he could answer we were plunged in sudden darkness. Someone had switched out the light that had been shining down through the hatchway. Before we knew it the opening to the hatchway had been closed.