as Roch?" I stammered.

"Yes, the document signed by you was found on the beach at St.
George----"

"In a keg, Lieutenant Davon, which I committed to the waters of the
lagoon."

"And which contained," went on the officer, "the notice by which we
were apprised that the island of Back Cup served as a refuge for Ker
Karraje and his band--Ker Karraje, this false Count d'Artigas, the
author of the double abduction from Healthful House."

"Ah! Lieutenant Davon----"

"Now we have not a moment to spare, we must profit by the obscurity."

"One word, Lieutenant Davon, how did you penetrate to the interior of
Back Cup?"

"By means of the submarine boat _Sword_, with which we have been
making experiments at St. George for six months past."

"A submarine boat!"

"Yes, it awaits us at the foot of the rocks. And now, Mr. Hart, where
is Ker Karraje's tug?"

"It has been away for three weeks."

"Ker Karraje is not here, then?"

"No, but we expect him back every day--every hour, I might say."

"It matters little," replied Lieutenant Davon. "It is not after Ker
Karraje, but Thomas Roch, we have come--and you also, Mr. Hart. The
_Sword_ will not leave the lagoon till you are both on board. If she
does not turn up at St. George again, they will know that I have
failed--and they will try again."

"Where is the _Sword_, Lieutenant?"

"On this side, in the shadow of the bank, where it cannot be seen.
Thanks to your directions, I and my crew were able to locate the
tunnel. We came through all right, and ten minutes ago rose to the
surface of the lake. Two men landed with me. I saw you issue from the
cell marked on your plan. Do you know where Thomas Roch is?"

"A few paces off. He has just passed me, on his way to his
laboratory."

"God be praised, Mr. Hart!"

"Amen, Lieutenant Davon."

The lieutenant, the two men and I took the path around the lagoon.
We had not gone far when we perceived Thomas Roch in front of us. To
throw ourselves upon him, gag him before he could utter a cry, bind
him before he could offer any resistance, and bear him off to the
place where the _Sword_ was moored was the work of a minute.

The _Sword_ was a submersible boat of only twelve tons, and
consequently much inferior to the tug, both in respect of dimensions
and power. Her screw was worked by a couple of dynamos fitted with
accumulators that had been charged twelve hours previously in the port
of St. George. However, the _Sword_ would s