"We have just looked into the cylinder," he announced, in a low voice.

"We found there enough gun-cotton to blow the 'Benson' into inch pieces.

It was a fearful crime to plan."

Jack Benson and Hal Hastings heard, but did not change color. There was no sense in losing nerve over a disaster that had been averted in time.

"The first thing to do, of course," continued Lieutenant Commander Kimball, "is to send instant word to Messrs. Trotter and Packwood.

They have a heap of work ahead of them."

"As to our own boat's crew," replied Jack, "I fancy the best thing we can do is to go back on board, since we can't do anything here. One of us will keep watch, and the rest of us can get some of a night's sleep yet."

"Why, yes, if you youngsters can sleep, after such happenings," laughed Kimball.

By this time Lieutenant Foster and two of his marines had followed the trail of footprints as far as the hard road. Here all trace was lost.

"What you want to do, Williamson," declared Jack, as soon as the submarine people were back on their own craft, "is to get into some dry clothes and make yourself a pot of hot coffee. Then get in between blankets for a sleep. I'll finish out your watch."

Nor was Benson alone in his watch, for a cutter from the gunboat, containing a corporal and two marines, beside sailors to row the boat, moved slowly around the submarine at a distance of fifteen or twenty yards.

After the rest had gone below, Captain Jack, hanging over the rail of the platform deck, saw other lanterns gleaming in and around the clump of bushes.

"That must be the Secret Service people, pulled out of their comfortable beds," mused Benson, smiling. "Won't they feel upset at any such thing happening hours after they've arrived on the spot?"

After Eph Somers had reported on deck to take his watch, Jack went below, once more dropping into sound slumber. The smell of coffee and bacon was wafted in from the galley when the young submarine captain next awoke.

"Well," announced Eph, as Jack and Hal came forward for their breakfast, "Trotter and Packwood haven't caught the fellows that laid the mine."

"It doesn't look strongly probable that they'll catch them, either,"

Jack replied. "I don't believe that the fellows who did that trick are any of the regular spies. For that matter, we now of only three spies here who are men. Drummond is under arrest, and so is Gaston. Neither of them could have had a hand in it. And there were two, so, if M.

Lemaire was in it, he had an unknown accomplice. But I don't believe M. Lemaire had any personal hand in laying that mine. I've a notion that he considers himself entirely too high cla.s.s to go into any mere blasting operations."

"'Mere blasting operations' is good," smiled Hal Hastings, "when we stop to think what those 'blasting operations' might have done for us if it hadn't been for Williamson."

"Anyone taking my name in vain?" demanded the machinist, smiling as he put in an appearance at that moment.

"We're trying to see," Eph explained, "whether we can do any better guessing than the Secret Service men as to the fellows who were kind enough to lay that mine under us last night."

"Got it figured out?" asked the machinist, as he transferred, a generous helping of bacon, eggs and fried potatoes, to his plate.

"For myself," put in Hal, "I'd suspect that fellow Gaston, in an instant, if he had only been at liberty. That fellow has an eye that looks like all the letters in the word 'r-e-v-e-n-g-e.'"

"That's so," nodded Jack, thoughtfully, as he ate. "But we happen to know that Gaston is very safe under lock and key. By the way, fellows, I don't suppose Mr. Farnum and Mr. Pollard have heard the news yet, or they'd be out here on the double quick."

After breakfast Jack went ash.o.r.e alone, to carry the exciting news to his employers. He found Messrs. Farnum and Pollard in the breakfast room at the Clayton. Both were astounded when they heard the news of the night's doings.

"Who on earth could have put up such a job against the submarine?"

gasped David Pollard.

"I don't know, sir," Captain Jack replied. "But I've left Hal on board, in command, and I mean to find out something about this business, if there is any way to do it."

With that he excused himself, rising and leaving the table at which his employers were seated.

Jacob Farnum gazed after his young submarine captain, then whispered to the inventor:

"That youngster has some notion in his head of where to look for the infernal criminals. And, ten to one, his idea is a good one that will bear fruit!"

CHAPTER XX

A BRIGHT LOOK AND A DEADLY WARNING

Jack's employer gave him rather too much credit in supposing that the boy had already worked out the problem of finding those who had made the attack on the "Benson."

As the submarine boy left the breakfast room he felt as much in the dark as ever. The only known spies who were still at large, for some reason known only to the Secret Service men, were M. Lemaire, Mlle. Nadiboff and Kamanako.

"This is rather earlier than either of that pair in the habit of showing themselves," muttered Benson, as the first two names crossed his thoughts. "I wonder whether I could get the least bit of an inkling by going to the jail and talking with Gaston? If I could bluff him into telling me anything, it might be so much gained. I might catch him off his guard, if I could get him angry enough."

Full of this interesting idea, the submarine boy strolled slowly along to the little jail, forming his plans as he went.

Arrived at the jail, Captain Jack found the keeper, as yet, in ignorance of the dastardly attempt that had been made on the submarine boat the night before. He listened, aghast, as Benson told him the whole story.

"Now, I've got a notion that Gaston's crowd are very likely at the bottom of this whole deal," continued the submarine boy, in a low tone.

"For one thing, while perhaps nothing much can be done to the other spies, this fellow, Gaston, is in here for a crime which, under the Florida laws, will go hard with him. It means that he'll be locked up for a few years. That may make both him and Lemaire ugly enough to put them up to almost any mischief. Was M. Lemaire here to see the fellow yesterday?"

"Lemaire has not been hero at all," replied the jailer.

"Was Mlle. Nadiboff here to see him yesterday?"

"No; she has been holding aloof. With the exception of his lawyer, the only people who ye been here to see Gaston were two fellows who came yesterday, about noon."

"Oho!" muttered Benson. "Who were they?"

The jailer turned to reach for a memorandum book.

"I keep the names given by all who come here to see prisoners, so I shall be able to answer you."

"Ah, here are the names. One fellow called himself Leroux, the other Stephanoulis."

"One name French, and the other Greek," muttered the submarine boy, thinking hard. "What did they look like?"

The jailer quickly and carefully described the pair. Jack listened attentively. Then rose, briskly.

"Did you hear any of the conversation they had with Gaston?"

"No."

"If they come again to-day can you lock them up and hold them?"