"It was not the tug, but a boat of the same kind that had got through the tunnel."

"A submarine boat?" I e.j.a.c.u.l.a.t.e.

"Yes, and manned by persons whose mission was to kidnap you and Thomas Roch."

"Kidnap us?" I echo, continuing to feign surprise.

"And," adds Engineer Serko, "I want to know what you think about the matter."

"What I think about it? Well, it appears to me that there is only one plausible explanation possible. If the secret of your retreat has not been betrayed--and I cannot conceive how you could have been betrayed or what imprudence you or yours could have committed--my opinion is that this submarine boat was exploring the bottom of the sea in this neighborhood, that she must have found her way into the tunnel, that she rose to the surface of the lagoon, that her crew, greatly surprised to find themselves inside an inhabited cavern, seized hold of the first persons they came across, Thomas Roch and myself, and others as well perhaps, for of course I do not know----"

Engineer Serko has become serious again. Does he realize the inanity of the hypothesis I try to pa.s.s off on him? Does he think I know more than I will say? However this may be, he accepts my professed view, and says:

"In effect, Mr. Hart, it must have happened as you suggest, and when the stranger tried to make her way out through the tunnel just as the tug was entering, there was a collision--a collision of which she was the victim. But we are not the kind of people to allow our fellow-men to perish before our eyes. Moreover, the disappearance of Thomas Roch and yourself was almost immediately discovered. Two such valuable lives had to be saved at all hazards. We set to work. There are many expert divers among our men. They hastily donned their suits and descended to the bottom of the lagoon. They pa.s.sed lines around the hull of the _Sword_----"

"The _Sword_?" I exclaim.

"That is the name we saw painted on the bow of the vessel when we raised her to the surface. What satisfaction we experienced when we recovered you--unconscious, it is true, but still breathing--and were able to bring you back to life! Unfortunately all our attentions to the officer who commanded the _Sword_, and to his crew were useless.

The shock had torn open the after and middle compartments, and they paid with their lives the misfortune--due to chance, as you observe--of having discovered our mysterious retreat."

On learning that Lieutenant Davon and his companions are dead, my heart is filled with anguish; but to keep up my role--as they were persons with whom, presumably, I was not acquainted, and had never seen--I am careful not to display any emotion. I must, on no account, afford ground for the suspicion that there was any connivance between the commander of the _Sword_ and me. For aught I know, Engineer Serko may have reason to be very skeptical about the discovery of the tunnel being accidental.

What, however, I am most concerned about is that the unlooked-for occasion to recover my liberty was lost. Shall I ever be afforded another chance? However this may be, my notice reached the English authorities of the archipelago, and they now know where Ker Karraje is to be found. When it is seen that the _Sword_ does not return to Bermuda, there can be no doubt that another attempt will be made to get inside Back Cup, in which, had it not been for the inopportune return of the tug, I should no longer be a prisoner.

I have resumed my usual existence, and having allayed all mistrust, am permitted to wander freely about the cavern, as usual.

It is patent that the adventure has had no ill effect upon Thomas Roch. Intelligent nursing brought him around, as it did me. In full possession of his mental faculties he has returned to work, and spends the entire day in his laboratory.

The _Ebba_ brought back from her last trip bales, boxes, and a quant.i.ty of objects of varied origin, and I conclude that a number of ships must have been pillaged during this marauding expedition.

The work on the trestles for Roch's engine goes steadily forward, and there are now no fewer than fifty engines. If Ker Karraje and Engineer Serko are under the necessity of defending Back Cup, three or four will be sufficient to render the island unapproachable, as they will cover a zone which no vessel could enter without being blown to pieces. And it occurs to me that they intend to put Back Cup in a state of defence after having argued as follows:

"If the appearance of the _Sword_ in the lagoon was due to chance the situation remains unchanged, and no power, not even England, will think of seeking for the _Sword_ inside the cavern. If, on the other hand, as the result of an incomprehensible revelation, it has been learned that Back Cup is become the retreat of Ker Karraje, if the expedition of the _Sword_ was a first effort against the island, another of a different kind--either a bombardment from a distance, or an attack by a landing party--is to be expected. Therefore, ere we can quit Back Cup and carry away our plunder, we shall have to defend ourselves by means of Roch's fulgurator."

In my opinion the rascals must have gone on to reason still further in this wise:

"Is there any connection between the disclosure of our secret--if it was, and however it may have been made--and the double abduction from Healthful House? Is it known that Thomas Roch and his keeper are confined in Back Cup? Is it known that the abduction was effected in the interest of Ker Karraje? Have Americans, English, French, Germans, and Russians reason to fear that an attack in force against the island would be doomed to failure?"

Ker Karraje must know very well that these powers would not hesitate to attack him, however great the danger might be. The destruction of his lair is an urgent duty in the interest of public security and of humanity. After sweeping the West Pacific the pirate and his companions are infesting the West Atlantic, and must be wiped out at all costs.

In any case, it is imperative that the inhabitants of Back Cup should be on their guard. This fact is realized, and, from the day on which the _Sword_ was destroyed, strict watch has been kept. Thanks to the new pa.s.sage, they are able to hide among the rocks without having recourse to the submarine tunnel to get there, and day and night a dozen sentries are posted about the island. The moment a ship appears in sight the fact is at once made known inside the cavern.

Nothing occurs for some days, and the latter succeed each other with dreadful monotony. The pirates, however, feel that Back Cup no longer enjoys its former security. Every moment an alarm from the sentries posted outside is expected. The situation is no longer the same since the advent of the _Sword_. Gallant Lieutenant Davon, gallant crew, may England, may the civilized nations, never forget that you have sacrificed your lives in the cause of humanity!

It is evident that now, however powerful may be their means of defence, even more powerful than a network of torpedoes, Engineer Serko and Captain Spade are filled with an anxiety that they vainly essay to dissemble. They hold frequent conferences together. Maybe they discuss the advisability of quitting Back Cup with their wealth, for they are aware that if the existence of the cavern is known means will be found to reduce it, even if the inmates have to be starved out.

This is, of course, mere conjecture on my part. What is essential to me is that they do not suspect me of having launched the keg that was so providentially picked up at Bermuda. Never, I must say, has Engineer Serko ever made any allusion to any such probability. No, I am not even suspected. If the contrary were the case I am sufficiently acquainted with Ker Karraje to know that he would long ago have sent me to rejoin Lieutenant Davon and the _Sword_ at the bottom of the lagoon.

The winter tempests have set in with a vengeance. The wind howls though the hole in the roof, and rude gusts sweep through the forest of pillars producing sonorous sounds, so sonorous, so deep, that one might sometimes almost fancy they were produced by the firing of the guns of a squadron. Flocks of seabirds take refuge in the cavern from the gale, and at intervals, when it lulls, almost deafen us with their screaming.

It is to be presumed that in such weather the schooner will make no attempt to put to sea, for the stock of provisions is ample enough to last all the season. Moreover, I imagine the Count d'Artigas will not be so eager in future to show his _Ebba_ along the American coast, where he risks being received, not, as. .h.i.therto, with the consideration due to a wealthy yachtsman, but in the manner Ker Karraje so richly merits.

It occurs to me that if the apparition of the _Sword_ was the commencement of a campaign against the island, a question of great moment relative to the future of Back Cup arises.

Therefore, one day, prudently, so as not to excite any suspicion, I ventured to pump Engineer Serko about it.

We were in the neighborhood of Thomas Roch's laboratory, and had been conversing for some time, when Engineer Serko touched upon the extraordinary apparition of an English submarine boat in the lagoon.

On this occasion he seemed to incline to the view that it might have been a premeditated expedition against Ker Karraje.

"That is not my opinion," I replied, in order to bring him to the question that I wanted to put to him.

"Why?" he demanded.

"Because if your retreat were known a fresh attempt, if not to penetrate to the cavern, at least to destroy Back Cup, would ere this have been made."

"Destroy it!" cried Serko. "It would be a dangerous undertaking, in view of the means of defence of which we now dispose."

"They can know nothing about this matter, Mr. Serko. It is not imagined, either in the new world or the old, that the abduction from Healthful House was effected for your especial benefit, or that you have succeeded in coming to terms with Thomas Roch for his invention."

Engineer Serko made no response to this observation, which, for that matter, was unanswerable.

I continued:

"Therefore a squadron sent by the maritime powers who have an interest in breaking up this island would not hesitate to approach and sh.e.l.l it. Now, I argue from this that as this squadron has not yet appeared, it is not likely to come at all, and that nothing is known as to Ker Karraje's whereabouts, and you must admit that this hypothesis is the most cheerful one, as far as you are concerned."

"That may be," Engineer Serko replied, "but what is, is. Whether they are aware of the fact or no, if warships approach within five or six miles of this island they will be sunk before they have had time to fire a single shot!"

"Well, and what then?"

"What then? Why the probability is that no others would care to repeat the experiment."

"That, again, may be. But these warships would invest you beyond the dangerous zone, and the _Ebba_ would not be able to put in to the ports she previously visited with the Count d'Artigas. In this event, how would you be able to provision the island?"

Engineer Serko remained silent.

This argument, which he must already have brooded over, was too logical to be refuted or dismissed, and I have an idea that the pirates contemplate abandoning Back Cup.

Nevertheless, not relishing being cornered, he continued:

"We should still have the tug, and what the _Ebba_ could not do, this would."

"The tug?" I cried. "But if Ker Karraje's secrets are known, do you suppose the powers are not also aware of the existence of the Count d'Artigas' submarine boat?"

Engineer Serko looked at me suspiciously.

"Mr. Hart," he said, "you appear to me to carry your deductions rather far."

"I, Mr. Serko?"