"They're still at it," exclaimed Merritt, as the flag continued its eccentric rises and falls; "what's next, I wonder?"

Dash--dash--dash--dash, spelled out the flag.

"That means 'to'," declared Rob.

"Yes, and there comes 'night'," exclaimed Merritt a moment later. "And now they've stopped. Let's see what message we've caught."

"Short and sweet," laughed Rob. "I guess we came in at the tail end of their confab. All we've got is 'Ready to-night'."

"Well, isn't that something?" demanded Merritt. "At all events it's a complete sentence and tells us that somebody will be ready for something to-night."

"Right you are, and that 'somebody' is to be Barton, I'll bet a doughnut."

"But ready for what?"

"That remains to be seen. I've always thought Barton would bear watching. I'm certain of it now, and if the submarine isn't mixed up in this tangle somewhere, call me a Chinaman."

"Are you going to tell the ensign about this?"

"Not till we have something more tangible to go upon. After all, we have proved nothing, but to-night we'll keep a close watch on Barton and in that way find out if our suspicions are correct or not."

And so it was arranged. The boys hunted a bit more, but somehow the strange signals and the peculiar behavior of Barton had got on their minds, and they gave up their sport earlier than they had expected and trudged back to camp to complete their arrangements for the night's work.

CHAPTER XVI.

SCOUTING FOR UNCLE SAM.

"Rob! Rob! Rob!"

Merritt nudged his dozing companion as they lay near to the submarine shed, where they had taken up their position earlier in the night.

Immediately after supper the lads had, apparently, slipped off to their tents; but as soon as they were sure that they were free from observation they had, in pursuance of their plans, taken up a position close to the sheltering place of the _Peacemaker_.

Rob had dozed off shortly before midnight, and the words at the beginning of this chapter formed Merritt's notification to him that it was time to bestir himself.

The boy, aroused at once from his nap, sat up at his comrade's summons.

"What is it?" he asked in a whisper.

"Look! Look yonder! Don't you see Barton sneaking toward the shed?"

There was no moon, but in the starlight Rob, thus admonished, could distinctly discern a shadowy figure gliding across the sand dunes to the submarine shed.

"It _is_ Barton, sure enough!" he exclaimed in a low, tense voice. "I guess we were right, Merritt, when we read that 'Ready to-night'

message."

"We sure were," was the response; "the question now is, what is that fellow up to?"

"Some sort of mischief, just as we surmised," was the reply. "Let's do an Indian crawl toward the shed and see what we can find out."

The next instant both boys were noiselessly wriggling their way on their stomachs toward the shed into the interior of which Barton had, by this time, vanished. It was easy work to make a noiseless advance over the soft sand, but so thoroughly had both the Boy Scouts practiced the maneuver of silent advance that even had the ground been different, it is likely that they could have approached unheard.

Right up to the very walls of the shed they wriggled their way and then, placing their eyes to a crack in the timbers, they peered in. By the yellow light of a lantern Barton had lighted they saw him dive down into the interior of the submarine and emerge, ere long, with several rolled sheets of paper.

The fellow did not appear to labor under anxiety that he was being watched, for he went boldly about his business, taking no apparent pains to screen the light or to move noiselessly. Having emerged from the submarine and reached once more the door of the shed, he extinguished the light and glided out into the night like a half-embodied form.

Merritt half leaped to his feet as he saw the fellow making off, but Rob drew his companion down into their place of concealment with a whispered,

"Hold on. Don't spoil everything now by betraying our presence. Let him get a little way and we'll follow him."

"But we may lose him in the darkness," objected Merritt.

"I scarcely think so," was the rejoinder; "in fact, I have a pretty good idea where he is bound for."

"And where may that be?"

"The place in which he lay this afternoon to read those signals from the distant island. Depend upon it, he is going to meet the men who manipulated that flag!"

"By hooky! That's so, Rob. What a mind you have for figuring out things!

Of course, it's plain enough now that he is betraying Mr. Barr by giving drawings and plans of the submarine to Mr. Barr's enemies, but I didn't think he'd take so bold a method."

"There's nothing very bold about it," retorted Rob. "He is a trusted man, and has been given every opportunity to be dishonest, if it so suits him."

"I guess that's right; but it's our duty to thwart him."

"You just bet it is, and we'll do it, too, if it's possible. See, there he goes over the top of that sand dune. I could see his figure silhouetted against the sky. I reckon it's safe now to take after him."

"All right, you say when."

"I'll give the word right here. Silently, now; remember he is on the outlook for some interference with his plans, and a false move may spoil everything."

"Don't worry about me. A first cla.s.s Scout should be able to carry through a simple little thing like this."

"Don't be too sure it's simple," admonished Rob, as they silently rose from their crouching postures and took after the vague shadow; "this thing may turn out to be bigger than we thought."

"Have you laid any plans as to what you will do if we do apprehend him in the act of transferring the plans to Mr. Barr's enemies?"

"Not yet. There's no use crossing a bridge till you come to it."

Through the night the boys pursued their quarry as silently as two snakes. At times they lost sight of him, but always his figure would loom up against the star-sprinkled sky as he topped a sand dune. At length they saw him pause and light the lantern, which he had used in the shed, and which he still carried.

This done, he swung the light twice across his body, after the fashion of a brakeman signalling a train to come ahead.

Instantly, out of the darkness, flashed an answering beacon--a red light. The boys clasped each other's arms. That they were on the brink of an exciting adventure they did not doubt. But in each lad's heart was a firm resolve that, come what might, they would do their duty by Uncle Sam.

"Was that red light shown from the other island?" whispered Merritt.