A touch on Joe Duncan’s shoulder served to arouse him, though he was in a deep sleep.  He sat up, demanding: 

“What is it?  Are we torpedoed?”

“No, but we may be,” was Blake’s low answer.  “Keep quiet and follow me.  Secor and Labenstein have both gone up on deck, I think.  We’d better follow.”

“Shall we tell Charlie?” asked Joe, as he slid from his berth.  Neither he nor his chums had taken off their clothes.

“Yes, I guess we’d better get him up,” Blake answered.  “If you and I have to watch these two fellows, we may need some one to send for help in case anything happens.  Come on, Macaroni,” he added, leaning over their helper and whispering in his ear.  “Wake up!”

Charles was up in an instant, a bit confused at first, as one often is when emerging from a heavy sleep, but he had his faculties with him almost at once, and was ready for action.

“What is it?” he asked, in a whisper.

In like low tones Blake told him, and then the three boys, after making sure by a cautious observation that neither of the suspected men was in sight, went out into the corridor and to the deck.

It was quite dark, for all unnecessary lights were dimmed, but there was a new moon, and the stars were bright, so that objects were fairly clear.  On either side could be dimly observed the black shapes of the convoying destroyers.

“Where are they?” asked Joe, in a whisper.  “The traitors!”

“I don’t know—­we’ll have to look,” was Blake’s answer.  They looked along the deck, but saw no one, and were about to turn to the other end of the craft when a figure stepped out from the shadow of a boat and sharply challenged them.

“Who are you—­what do you want?” was asked.

It was one of the ship’s crew assigned to night-watch.  Blake knew him slightly, having, at the man’s request one day, showed him something of the workings of a moving picture camera.

“We came up looking for two gentlemen who have the staterooms opposite ours,” Blake answered, resolving to “take a chance” in the matter.  “Lieutenant Secor and Mr. Labenstein,” he added.  “Have you seen them?”

“Yes; they came up to get a bit of air, they said,” answered the sailor.  “I saw them a little while ago.  You will find them up near the bow.  Do not show a light, whatever you do, and light no matches.  If you wish to smoke you must go below.”

“Thanks, we don’t smoke,” Joe answered, with a low laugh.  “But we’ll be careful about lights.”

“All right,” answered the sailor.  “We have to look out for submarines, you know,” he added.  “This is the worst part of the danger zone.”

The boys moved forward like silent shadows, peering here and there for a sight of the two figures who had come up a little while before them, with evil intentions in their hearts they had no doubt.  Even now there might be flashing across the dark sea, from some hidden vantage point on the ship, a light signal that would mean the launching of the deadly torpedo.