For a moment there was more terror and excitement aboard the Jeanne, if it were possible, after it became certain that another craft, the nature of which none knew, was headed toward the French steamer. Then an officer gifted with sound common-sense, cried out in English, so that the majority could understand:

"It is a destroyer! It is a destroyer belonging to the Stars and Stripes coming to our rescue. Three cheers!"

Nobody gave the three cheers, but it heartened every one to hear them called for, and the real meaning of the smoke was borne to all.

"Of course it can't be a submarine!" exclaimed Blake. "They don't send out any smoke, and there aren't any other German boats at sea. It's a destroyer!"

"One of ours, do you think?" asked Charlie.

"Perhaps. Uncle Sam has a lot of 'em over here to act as convoys. Probably this is our escort coming up a little late to the ball," said Joe.

"But we did very well by ourselves," observed Blake. "It was a narrow squeak, though."

And indeed it was a narrow escape. The Jeanne had, unaided, driven off the undersea boat, and perhaps had damaged her by the rain of shot and shell poured at her steel sides. They could not feel sure of this, though, for the approach of the destroyer was probably known to the submarine, for they have underwater telephones which tell them, by means of the throbbing of the screws and propellers in the water, just about how far away another ship is, and what speed she is making, as well as the direction from which she is coming.

Whether the submarine had expended her last torpedo, or whether having missed what she intended for a vital shot she deemed there was not time to launch another and had sunk out of sight, or whether she were disabled, were questions perhaps never to be answered.

At any rate, the approach of the destroyer, which came on with amazing speed, served to make the Jeanne comparatively safe. The lifeboats were emptied of their passengers, and once more there was a feeling of comparative safety as the passengers again thronged the decks.On came the destroyer. She proved to be one of Uncle Sam's boats, and the joy with which she was greeted was vociferous and perhaps a little hysterical. She had learned by wireless of the appearance of the French craft in the danger zone, and had come to fulfill her mission. She had been delayed by a slight accident, or she would have been on hand when the submarine first approached.

The wireless message that had come just as the German craft appeared had been from the destroyer, to bid those aboard the Jeanne have no fear, for help was on the way. And soon after the grim and swift craft from the United States had begun to slide along beside the Jeanne two more destroyers, one of them British, made their appearance, coming up with the speed of ocean greyhounds.

There was great rejoicing among the passengers, and much credit was given the lookout for his promptness in reporting a sight of the submarine. Formal thanks were extended to the gun crews for their efficient work, without which the undersea boat might have accomplished her purpose. Nor were the boiler room and engineer forces forgotten, for it was because of the sudden burst of speed on the part of the Jeanne that she escaped that one torpedo at least.

"Now we'll be all right," Charlie said, as he helped his friends make a few pictures of the approach and the convoying of the destroyers to add to the views they had of the submarine and her defeat—temporary defeat it might prove, but, none the less, a defeat.

"Well, hardly all right," remarked Blake, as the camera was dismounted. "We're still in the danger zone, and the Huns won't let slip any chance to do us harm. But I guess we have more of a chance for our white alley than we had before."

Though the French ship was now protected by the three convoying vessels, the crews of which kept a sharp watch on all sides for the presence of more submarines, there was still plenty of danger, and this was felt by all.

At any moment a submarine, approaching below the surface with only her periscope showing—and this made a mark exceedingly hard to see and hit—might launch a torpedo, not only at the merchant-man but at one of the destroyers.

"It's like sleeping over a case of dynamite," observed Joe, as he and his chums went below. "I'd rather be on the war front. You can at least see and hear shells coming."

"That's right," agreed Blake. "Well, if nothing happens, we'll soon be there now."

"If is a big word these days," observed Charlie.

"Now that we're comparatively safe for the moment, I want to ask you fellows something," said Blake, after a pause.

"Ask ahead," returned Joe. "If you want to know whether I was scared, I'll say I was, but I was too busy getting pictures to notice it. If it is something else——"

"It is," interrupted Blake, and his manner was grave. "Come below and I'll tell you. I don't want any one else to hear."

Wondering somewhat at their friend's manner, Joe and Charlie went to their stateroom, and there Blake closed the door and took the dark cloth down from the mirror. A look into it showed that the transom of the room opposite—the cabin of Levi Labenstein—had been closed.

"So we can't tell whether he's in there or not," said Blake.

"Did you want to talk about him?" asked Joe.

"Yes, him and the lieutenant. Did you fellows happen to notice what they were doing when the submarine was attacking us?"

"Not especially," answered Joe. "I did see Lieutenant Secor looking at us as we worked the camera, but I didn't pay much attention to him."

"It wasn't him so much as it was the German," went on Blake.

"In what way?"

"Did you see where he was standing when the submarine came out of the water?"

Neither Joe nor Charlie had done so, or, if they had, they did not recall the matter when Blake questioned them. So that young man resumed:

"Well, I'll tell you what I saw: Labenstein was leaning over the rail on the side where the submarine showed, and he was holding a big white cloth over the side."

"A big white cloth?" cried Joe.

"That's what it was," went on Blake. "It looked to me like a signal."

"Do you mean a signal of surrender?" asked Charlie. "A white flag? He wouldn't have any right to display that, anyhow. It would have to come from Captain Merceau."

"Maybe he meant that he'd surrender personally," suggested Joe, "and didn't want his fellow-murderers to hurt him."

"I don't know what his object was," went on Blake, "but I saw him take from his pocket a big white cloth and hold it over the side. It could easily have been seen from the submarine, and must have been, for he displayed it just before the underwater boat came up."

"A white cloth," mused Joe. "From his pocket. Was it his handkerchief, Blake?"

"He wouldn't have one as large as that, even if he suffered from hay fever. I think it was a signal."

"A signal for what?" Charlie again asked.

"To tell the submarine some piece of news, of course—perhaps the port of sailing, something of the nature of our cargo, or perhaps to tell just where to send the torpedo. I understand we are carrying some munitions, and it may be that this German spy directed the commander of the submarine where to aim the torpedo so as to explode them."

"But he'd be signaling for his own death warrant!" cried Joe.

"Not necessarily," answered Blake. "He may have had some understanding with the submarine that he was to be saved first. Perhaps he was going to jump overboard before the torpedo was fired and was to be picked up. Anyhow, I saw him draping a white cloth over the side, and I'm sure it was a signal."

"Well, I guess you're right," said Joe. "The next question is, what's to be done? This fellow is a spy and a traitor, and we ought to expose him."

"Yes," agreed Blake. "But we'd better have a little more evidence than just my word. You fellows didn't see what I saw, that's plain, and perhaps no one else did. So it would only make a big fuss and not result in anything if I told the captain."

"Then what are you going to do?" asked Charlie.

"Just keep watch," Blake answered.

"What about Lieutenant Secor?" asked Joe.

"Well, I didn't see him do anything," admitted Blake. "Though I have my suspicions of him also. He and Labenstein weren't talking so earnestly together for nothing. We'll watch that Frenchman, too."

"And if he tries any more games in spoiling films I'll have my say!" threatened Macaroni.

The boys talked the situation over at some length as they put away the films they had taken of the submarine attack, and agreed that "watchful waiting" was the best policy to adopt. As Blake had said, little could be gained by denouncing Labenstein with only the word of one witness to rely on.

"If all three of us catch him at his traitorous work, then we'll denounce him," suggested Blake.

"Yes, and the Frenchman, too!" added Charlie, in a louder voice, so that Blake raised a cautioning hand.

At that moment came a knock on their door, and a voice said:

"I am Mr. Labenstein!"