interposed Hal.

"Then what would you do?" demanded Mr. Farnum, turning upon the young engineer.

"If Jack has come to any misadventure through that pair of spies,"

uttered Hal, anxiously, "it seems to me it will be a heap more promising if we keep a sharp, unseen watch over every move made by M. Lemaire and Mlle. Nadiboff."

"Right-o, every time!" clicked Eph. "If anything has happened to good old Jack through that pair, then they're the only ones to be watched!"

Dinner, that evening, wasn't as confident a meal for the submarine party as luncheon had been. Both Mlle. Nadiboff and the Frenchman were in the dining room, though they did not sit together.

Later, the young Russian woman appeared in the ballroom. She was as eagerly sought as a partner as she had been the night before.

Farnum and his friends did not enter the ballroom, not having brought evening dress ash.o.r.e with them.

Yet, some of the time, they remained near the entrance to the ballroom.

It was here that M. Lemaire, in evening clothes, saw them and bowed most amiably.

"You do not care for the gaiety of the dance?" he inquired.

"No," replied Jacob Farnum, evasively. "We are looking for Captain Benson, and thought it just possible he had entered the ballroom."

"Did he not tell you, this afternoon, whether he would be at the dance?"

Lemaire inquired, in a tone of polite curiosity only.

"We didn't see him this afternoon," replied Mr. Farnum, rather curtly.

"You astonish me," cried the Frenchman.

"In fact we have not seen Captain Benson since we left him on an automobile ride this morning."

"Ah! I had not heard of that," murmured the Frenchman. "I trust nothing is wrong with the gallant young fellow."

"Oh, that's hardly likely," drawled Jacob Farnum, with an effort.

"Captain Jack Benson a lad with a pretty good idea of how to take care of himself."

While speaking Farnum did not look particularly at the Frenchman, but trusted to the boys to watch the man's face covertly. M. Lemaire, however, proved to be a good actor and a master of facial expression.

As soon as he could, without attracting attention, Jacob Farnum drew his little force to one side.

"Something serious has happened to Jack," muttered the shipbuilder, moodily. "It may have been an accident, but I believe it's ten times more likely that that infernal gang of spies have trapped the lad and brought harm to him. We've got to act, and act fast!"

CHAPTER XII

IN THE POWER OF THE SPIES

Something had, indeed, "happened" to Jack Benson, and much more was likely to happen.

The young submarine captain lay on a pile of dried gra.s.s that had been thrown on a board floor. His hands were still manacled. Worse, one of his feet now had an ankle-ring fastened securely, and this was chained to a stout staple driven in the floor.

It was a curious place in which young Benson lay, a place with a strange history.

Years before a tunnel had been bored into the side of a hill. After the tunnel had been lined with a masonry of stone it was not more than three feet in diameter. This tunnel led into an artificial cave some eighteen feet square and nine feet high. This cave had been sh.o.r.ed up and boarded as to ceiling, floor and walls.

A great deal of labor had been 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 sh.o.r.e 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're trying to work any ghostly trick on me," called Benson, derisively, "try something else!"

Again the groan, a bit louder, but Jack's answer was a merry, ringing laugh, in which there, was not a trace of dread.

"Thank you for the company, Mr. Groan," he called cheerily. "I was beginning to feel a bit lonely. But say! Can't you bring a light--even a ghostly one?"

"I am the spirit of Paul Jones," breathed a low, wailing voice.

"Oh nonsense!" jeered Jack. "Paul Jones never spoke with a cheap French accent."

"I come to--to warn--you," sounded the same sepulchral accents.

"Bring the warning right in and let's have look at it," begged Jack, heartily. Some convulsive sobs sounded out by the pa.s.sageway.

"Oh, say," chuckled Jack, "as a vender of blood curdling noises you're in need of repairs. Listen! I'll sound a much better line for you!"

With that, and in a deep, blood curdling voice, Captain Benson started in on the first verse of "Down among the dead men."

He was interrupted then by a more tangible sound. Beyond, a match was scratched. Then a lantern was thrust in from the low tunnel, followed by the appearance of the rather long body of Gaston, the chauffeur.

"I thought my singing would bring something," chuckled Jack. "In a large town it always brings the police. Well, how are you? I'm really glad to see anything human, and I suppose you'll answer to that description, eh?"