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 shell
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?"

"Yes, and I think you talk about all this like a man who knows more
than he ought to."

This remark brought me up abruptly. It was evident that my arguments
might give