The latter man spoke low, too.  The other had a bluff and coarse voice.  He was a typical old sea-dog in his way.  Only, a German sea-dog!

“Are you going back there yet?” Whistler heard him ask.

“For just one thing.  You know what that is, Braun.”

“Ach! Yes.”

“My work is done there,” said the man, Blake, with pride in his voice.  “Oh, it will be taken note of, don’t fear.”

“I bet you!” growled the other, in evident admiration.  “Undt so she goes oop, yes?  Boom!”

“Sh!” warned the other.  “Never mind any talk about it.”

But the other was inclined to be voluble.  Whistler thought the skipper of the oil tender, Braun, had been drinking.  “And when alcohol is in the brain wit is very likely to move out,” he muttered.

“Grand work!” he ejaculated. “Ach, yes!  Undt there will be more grand work when two-fifty is joined by the others.”

“Sh!” warned Blake again.  “You talk too much, Braun.  The wise man keeps a still tongue.”

Ordinarily Whistler Morgan would have found nothing in this overheard conversation to fan suspicion into a blaze.  He quite realized this fact.  But what he had seen at Elmvale, and the presence of Blake on the oil tender, led in his mind to but one conclusion.

Blake and his companion referred to the former’s work in Elmvale.  And what was that work?  Not merely the peaceful occupation of chemist in the laboratory of the munition factory.  He was convinced that Blake referred to something entirely different when he said:  “My work is done there.”

Nor was Blake merely an inventor, hiding away the actual working model of an invention until he could secure its patent, for instance.  No, indeed!

Yet Morgan could not imagine what that water wheel was for.  To what end could it have been placed under the rock on the edge of the overflow-stream from the Elmvale Dam?

Whistler had little to say himself during that meal at Yancey’s.  He heard nothing more from the next booth, for Blake seemed to manage the half drunken skipper of the Sarah Coville with better judgment.  By and by the two men left the restaurant.

“Say! are we going to follow them?” asked the excited Frenchy.

“Aw, you poor fish!” scoffed Torry.  “Where’d we follow them to?  Back to that stinking oiler?  And how would we follow them to sea?  We haven’t a boat.”

“That’s so,” Frenchy admitted, crestfallen.

“No good to try to keep tabs on them,” admitted Phil.  “I hope Ensign MacMasters will pick up news of that boat again.  Just think of his chaser coming right in here and not seeing the oiler in the fog.  Tough luck!”

“Say!” queried Ikey, “what did you hear, Whistler?”

“Just about what you did,” returned the older lad.  “Nothing much.”

“What are we going to do?” demanded Torry.

“Pay our bills and go to the train.  It is almost time,” said Whistler rather grumpily.