“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.”