“What have you to tell me about Mr. Blake, anyway?  I don’t want to hear a lot of inconsequential gossip.  I am worried about the man.”

“Yes, sir.  So am I,” declared Whistler very earnestly.  “I’ve been worried about him ever since the other day when we fellows were over here trying to get some of the boys to enlist in the Navy.”

“Ah, were you one of that crowd?” asked Mr. Santley.

“Yes, sir; and coming over here we saw that man Blake——­”

He went on to tell the manager of the munition factory about how his suspicions were aroused and about the water wheel he had found at the foot of the dam, ending with a detailed account of the affair of the oil tender.

Mr. Santley’s face expressed nothing but lively curiosity.

“And to-day you saw him on a boat that you think is a feeder for German submarines?” muttered the manager.  “It is whispered that they are off this coast.”

“We overheard this Blake and a man who I’m sure is captain of that oil boat talking in a restaurant to-night.  They mentioned two-fifty which I believe is the number of the submarine off this coast.  They spoke as though more were expected.  The Germans are going to make a big drive on our shipping over here.”

“You may be right, boy,” agreed Mr. Santley.  “That man Blake—­well, he doesn’t seem to be in Elmvale now.”

“He came back on this evening’s train,” declared Whistler.

“Are you sure?  I have been waiting for him to show up here,” cried Mr. Santley.  “To tell the truth, young man, I have discovered some things here that I want him to explain.  For one thing, I have picked up a letter in his locker which is addressed to him, it is evident, but not by the name of Blake.  It is written in German and I want it explained.”

“Oh, Mr. Santley!” cried Whistler, “I believe there is something wrong.  He told that Captain Braun, of the Sarah Coville, that his work was finished here.  He was only returning for a particular thing to Elmvale.”

“But he hasn’t come here!” exclaimed Mr. Santley.  “And he has some private property in the office.”

“Maybe he isn’t coming here,” breathed the boy.  “Maybe he is only going up to the dam!”

“To the dam?”

“That water-wheel business!  It perplexes me,” explained Whistler Morgan.

“We’ll go up there and take a look!” exclaimed Mr. Santley, grabbing his hat and banging down the roll top of his desk and locking it.  “You’ve got me all stirred up now, boy.”

They hurried out of the office.  Mr. Santley spoke in a low voice to the armed guard on the front steps.

“If Blake comes here, hold him till I return,” he said.  “Do you understand? Hold him—­even if you have to knock him down and sit on him.”

“All right, sir,” said the man, nodding grimly.

Mr. Santley started down the steps after the excited Whistler, who was already getting into the automobile, the engine of which was still running.  At that instant the night was as peaceful as could be.  The valley below the high dam lay quietly under the light of the stars, and a pale moon was just rising above the treetops.