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 suffice to take us out of this prison, to restore us to liberty--that liberty of which I had given up all hope. Thomas Roch was at last to be rescued from the clutches of Ker Karraje and Engineer Serko. The rascals would not be able to utilize his invention, and nothing could prevent the warships from landing a storming party on the island, who would force the tunnel in the wall and secure the pirates!

We saw no one while the two men were conveying Thomas Roch to the _Sword_, and all got on board without incident. The lid was shut and secured, the water compartments filled, and the _Sword_ sank out of sight. We were saved!

The _Sword_ was divided into three water-tight compartments. The after one contained the accumulators and machinery. The middle one, occupied by the pilot, was surmounted by a periscope fitted with lenticular portholes, through which an electric search-lamp lighted the way through the water. Forward, in the other compartment, Thomas Roch and I were shut in.

My companion, though the gag which was choking him had been removed, was still bound, and, I thought, knew what was going on.

But we were in a hurry to be off, and hoped to reach St. George that very night if no obstacle was encountered.

I pushed open the door of the compartment and rejoined Lieutenant Davon, who was standing by the man at the wheel. In the after compartment three other men, including the engineer, awaited the lieutenant's orders to set the machinery in motion.

"Lieutenant Davon," I said, "I do not think there is any particular reason why I should stay in there with Roch. If I can help you to get through the tunnel, pray command me."

"Yes, I shall be glad to have you by me, Mr. Hart."

It was then exactly thirty-seven minutes past eight.

The search-lamp threw a vague light through the water ahead of the _Sword_. From where we were, we had to cross the lagoon through its entire length to get to the tunnel. It would be pretty difficult to fetch it, we knew, but, if necessary, we could hug the sides of the lake until we located it. Once outside the tunnel the _Sword_ would rise to the surface and make for St. George at full speed.

"At what depth are we now?" I asked the lieutenant.

"About a fathom."

"It is not necessary to go any lower," I said.