"The tug! The tug!" I exclaimed. "Lieutenant, here is the tug returning to Back Cup!"

"Full speed astern," ordered the officer, and the _Sword_ drew back just as she was about to enter the tunnel.

One chance remained. The lieutenant had swiftly turned off the light, and it was just possible that we had not been seen by the people in the tug. Perhaps, in the dark waters of the lagoon, we should escape notice, and when the oncoming boat had risen and moored to the jetty, we should be able to slip out unperceived.

We had backed close in to the south side and the _Sword_ was about to stop, but alas, for our hopes! Captain Spade had seen that another submarine boat was about to issue through the tunnel, and he was making preparations to chase us. How could a frail craft like the _Sword_ defend itself against the attacks of Ker Karraje's powerful machine?

Lieutenant Davon turned to me and said: "Go back to the compartment where Thomas Roch is and shut yourself in. I will close the after-door. There is just a chance that if the tug rams us the water-tight compartments will keep us up."

After shaking hands with the lieutenant, who was as cool as though we were in no danger, I went forward and rejoined Thomas Roch. I closed the door and awaited the issue in profound darkness.

Then I could feel the desperate efforts made by the _Sword_ to escape from or ram her enemy. I could feel her rushing, gyrating and plunging. Now she would twist to avoid a collision. Now she would rise to the surface, then sink to the bottom of the lagoon. Can any one conceive such a struggle as that in which, like two marine monsters, these machines were engaged in beneath the troubled waters of this inland lake?

A few minutes elapsed, and I began to think that the _Sword_ had eluded the tug and was rushing through the tunnel.

Suddenly there was a collision. The shock was not, it seemed to me, very violent, but I could be under no illusion: the _Sword_ had been struck on her starboard quarter. Perhaps her plates had resisted, and if not, the water would only invade one of her compartments, I thought.

Almost immediately after, however, there was another shock that pushed the _Sword_ with extreme violence. She was raised by the ram of the tug which sawed and ripped its way into her side. Then I could feel her heel over and sink straight down, stern foremost.

Thomas Roch and I were tumbled over violently by. this movement. There was another b.u.mp, another ripping sound, and the _Sword_ lay still.

Just what happened after that I am unable to say, for I lost consciousness.

I have since learned that all this occurred many hours ago.

I however distinctly remember that my last thought was:

"If I am to die, at any rate Thomas Roch and his secret perish with me--and the pirates of Back Cup will not escape punishment for their crimes."

CHAPTER XV.

EXPECTATION.

As soon as I recover my senses I find myself lying on my bed in my cell, where it appears I have been lying for thirty-six hours.

I am not alone. Engineer Serko is near me. He has attended to me himself, not because he regards me as a friend, I surmise, but as a man from whom indispensable explanations are awaited, and who afterwards can be done away with if necessary.

I am still so weak that I could not walk a step. A little more and I should have been asphyxiated in that narrow compartment of the _Sword_ at the bottom of the lagoon.

Am I in condition to reply to the questions that Engineer Serko is dying to put to me? Yes--but I shall maintain the utmost reserve.

In the first place I wonder what has become of Lieutenant Davon and the crew of the _Sword_. Did those brave Englishmen perish in the collision? Are they safe and sound like us--for I suppose that Thomas Roch has also survived?

The first question that Engineer Serko puts to me is this:

"Will you explain to me what happened, Mr. Hart?"

Instead of replying it occurs to me to question him myself.

"And Thomas Roch?" I inquire.

"In good health, Mr. Hart." Then he adds in an imperious tone: "Tell me what occurred!"

"In the first place, tell me what became of the others."

"What others?" replies Serko, glancing at me savagely.

"Why, those men who threw themselves upon Thomas Roch and me, who gagged, bound, and carried us off and shut us up, I know not where?"

On reflection I had come to the conclusion that the best thing to do was to pretend that I had been surprised before I knew where I was or who my aggressors were.

"You will know what became of them later. But first, tell me how, the thing was done."

By the threatening tone of his voice, as he for the third time puts this question, I understand the nature of the suspicions entertained of me. Yet to be in the position to accuse me of having had relations with the outside he would have had to get possession of my keg. This he could not have done, seeing that it is in the hands of the Bermudan authorities. The pirates cannot, I am convinced, have a single proof to back up their suspicions.

I therefore recount how about eight o'clock on the previous evening I was walking along the edge of the lagoon, after Thomas Roch had pa.s.sed me, going towards his laboratory, when I felt myself seized from behind; how having been gagged, bound, and blindfolded, I felt myself carried off and lowered into a hole with another person whom I thought I recognized from his groans as Thomas Roch; how I soon felt that I was on board a boat of some description and naturally concluded that it was the tug; how I felt it sink; how I felt a shock that threw me violently against the side, and how I felt myself suffocating and lost consciousness, since I remember nothing further.

Engineer Serko listens with profound attention, a stern look in his eyes and a frown on his brow; and yet he can have no reason that authorizes him to doubt my word.

"You claim that three men threw themselves upon you?" he asks.

"Yes. I thought they were some of your people, for I did not see them coming. Who were they?"

"Strangers, as you must have known from their language."

"They did not utter a word!"

"Have you no idea as to their nationality?"

"Not the remotest."

Do you know what were their intentions in entering the cavern?"

"I do not."

"What is your opinion about it?"

"My opinion, Mr. Serko? I repeat I thought they were two or three of your pirates who had come to throw me into the lagoon by the Count d'Artigas' orders, and that they were going to do the same thing to Thomas Roch. I supposed that having obtained his secrets--as you informed me was the case--you had no further use for him and were about to get rid of us both."

"Is it possible, Mr. Hart, that you could have thought such a thing!"

continued Serko in his sarcastic way.

"I did, until having been able to remove the bandage from my eyes, I perceived that I was in the tug."