After ten minutes of the most painful suspense that any of the boys had ever known, the three sailors returned with the report that while one of the forward plates was bent and was leaking slightly, there appeared to be no danger.

Mr. Barr made no secret of his relief at receiving this bit of information. The boys burst into a cheer, and Barton, crouching in cowardly panic in the engine room, knew by this sound that all was well.

"Now we'll get to the surface quick and see what happened," declared the inventor.

The Peacemaker, which all this time had been slowly backing, was sent upward once more. As soon as they reached the surface Mr. Barr opened the conning tower hatch, and they all hastened out on deck. To their amazement the water all about was dyed crimson, and the cause was almost immediately apparent. Not far off lay the carcass of a whale, almost cut in two. This was beyond question the obstacle that the submarine had struck. Probably the dead cetacean could not get out of the way of the steel diving craft in time, or else deemed it another whale, and so was rammed by the sharp steel prow.

"Suppose that had been a solid object, like a rock, or a submerged derelict?" asked Rob.

"We shouldn't be here now," rejoined Ensign Hargreaves calmly enough, but in his voice there was palpable evidence of the relief he felt at their narrow escape.

"I guess we'll stay on the surface for a while now," decided the inventor. Accordingly, the craft was put about and headed for the island at a good rate of speed. The return voyage was made without incident, except that Tubby caused much amusement by inquiring if whale flesh was edible, and if it was, he should enjoy a broiled whale steak for dinner.

When the shed was reached the bow of the submarine was elevated by means of powerful geared tackle provided for this purpose, and the job of substituting a new plate for the damaged one was begun. It was finished by sunset.

That afternoon Rob and Merritt took the shotguns and started for the other shore of the island to see if they could not bring down some shore birds. They tramped along the beach and met with some success. Their walk brought them to the opposite shore of the island, as has been said, and they found themselves in a desolate stretch of country, nothing but sand and brush and coarse shore grass.

They were discussing the odd nature of their mission on the island, when Merritt suddenly grasped his companion's arm and pointed seaward, toward another of the islands that have been mentioned as being scattered pretty closely in the vicinity. Rob was just in time to catch sight of a motor boat, seemingly a fast one, slipping behind the spot of land.

At the same instant a figure rose from the grass almost in front of them. It was Barton the machinist. He had apparently been concealed in the grass, and had not calculated on the boys discovering him.

"Well, what are you after now? Spying on me again, eh?" he snarled angrily.

"I don't know why you should say we were spying on you," rejoined Rob, "unless you are up to something wrong."

"What do you mean?" asked Barton, stepping quickly toward him as if to strike him.

The man's hand was upraised, but the determined way in which Rob met his angry glare caused him to drop it.

"I want you to quit followin' me around, that's all," he said.

"I guess this island's big enough to hold all of us," snapped Merritt, "and as for following you around, we have other and better occupations on our hands."

The machinist made an angry reply and set off across the island at a rapid pace. As he did so an odd incident took place on the island behind which the motor boat had vanished.

On a staff which the boys had not previously noticed a red flag began to glide up and down. Sometimes it was hoisted quickly and then again slowly.

"What in the world are they doing over there?" wondered Merritt.

"I can't make out unless they are a party of crazy campers amusing themselves," rejoined Rob; and then he suddenly burst out: "By Jove, I have it; they are signalling."

"But signalling what or who?"

"I haven't decided yet; but I wonder if the same thought has occurred to you as to me?"

"Namely, what?"

"Why, that Barton was watching those signals."

"You mean that they were intended for him?"

"That's what."

"But what would they be signalling him for?"

"Only one thing that I can think of. You know what the ensign said about spies; well, if that fellow Barton isn't up to some crooked work, why should he sneak off like this and be so anxious to hide from us when we happen along accidentally? Then, too, there's that paper covered with drawings that I found in the engine room."

"By ginger, I see what you are driving at. You think that Barton is a traitor, and is in league with those spies?"

"It's a grave accusation to make, but I can hit on no other explanation of his actions. He is angry at us because he thinks we may see too much. Look, they are still signalling."

"I wish we could read what they are saying."

"I think I can," rejoined Rob quietly.

"You can?"

"Yes."

"How are you going to do it?"

"By bringing my knowledge of Morse into play. I think that when the flag is run up slowly it means a dash and a quick run is a dot. Let's try it anyway."

Luckily the spot where the two boys were was grown with high, coarse grass, and the sand dunes rose high in places, affording protection for them.

As the flag rose and fell they spelled out a word according to the Morse code.

"That's 'Ready'," proclaimed Rob exultingly; "we have hit on their code, all right."

"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.