en expended in building this curious place
under a low hill. Yet the original builders had figured that their time
so spent would yield large returns. This part of the Florida coast lay
conveniently near to Cuba. On moonless nights a small sailing craft
would put in along the coast, laden with smuggled Havana cigars. There
being no safe place along the shore in which to store the cigars, this
place, hidden well in a forest, had been constructed as a safe
depository. For some time the cigar smugglers had prospered. Then, as
was to have been expected, Uncle Sam's sharp eyed customs men ran the
illegal business down, arresting the smugglers, all of whom were
subsequently imprisoned.

For a while afterwards this cave had been visited by the curious. All
this smuggling, however, was now a thing of many years past, and
curiosity-seekers had come to leave the place alone.

M. Lemaire, however, in studying the surrounding country, had heard of
the artificial cave. He visited it. At need, he saw that it would suit
his purposes. And now Jack Benson lay there, having been brought hither
in Mlle. Nadiboff's automobile.

The young submarine captain was now not gagged. He had yelled for help
perhaps two hundred times in the long hours since his enemies had left
him there. Yet there had been no response. Benson was now willing to
believe that there was now no likelihood whatever of his being able to
summon help.

Unable to consult his watch, and lying there in complete darkness, the
submarine boy had lost track of time. It was now nearly two in the
morning. He had not eaten since early the morning before. He was
famished, and, what was much worse, was parched for want of a drink
of water.

"I wonder if they intend to leave me here to die?" thought Jack Benson,
for perhaps the five-hundredth time. "It would be fiendish. Yet
looking for mercy in Lemaire would be like looking for a lake of pure
water in the Sahara."

Jack shifted, as much as the chain at ankle would permit. He groaned
with the discomfort of it all.

As if in answer there came another groan, low, hollow, yet unmistakable.
Captain Jack raised himself on one elbow, listening keenly. The groan
was repeated.

"Who's there?" he called.

By way of answer there came still another groan. It was hollow,
gruesome, and suggested the grave itself. But Jack Benson was a
healthy, intelligent boy, with sound digestion and well tuned nerves.

"If you'r