Watchful guard was maintained night and day against an attack by submarines, and though there were several alarms, they turned out to be false.  And in due season, the vessel arrived at “an English port,” as the papers stated.

“Let’s go and see if Captain Merceau wants us to give any evidence against those fellows,” suggested Joe; and this seemed a good plan to follow.

“Ah, yes, my American friends!” the commander murmured, as the boys were shown into his cabin.  “What can I do for you?”

“We thought we’d see if you wanted us in relation to the arrest of Secor and Labenstein,” answered Blake.

“Ah, yes!  The two men who signaled the submarine.  I have had them under surveillance ever since you made your most startling disclosures.  I sent a wireless to the war authorities here to come and place them under arrest as soon as the vessel docked.  I have no doubt they are in custody now.  I’ll send and see.”

He dispatched a messenger who, when he returned, held a rapid conversation with the captain in French.  It was evident that something unusual had taken place.

The captain grew more excited, and finally, turning to the boys, said in English, which he spoke fluently: 

“I regret to tell you there has been a mistake.”

“A mistake!” cried Blake.

“Yes.  Owing to some error, those men were released before the war authorities could apprehend them.  They have gone ashore!”

CHAPTER XIII

UNDER SUSPICION

Blake, Joe and Charles looked at one another.  Then they glanced at Captain Merceau.  For one wild moment Blake had it in mind to suspect the commander; but a look at his face, which showed plainly how deeply chagrined he was at the failure to keep the two under surveillance, told the young moving picture operator that there was no ground for his thought.

“They got away!” repeated Joe, as though he could hardly believe it.

“Yes, I regret to say that is what my officer reports to me.  It is too bad; but I will at once send out word, and they may be traced and apprehended.  I’ll at once send word to the authorities.”  This he did by the same messenger who had brought the intelligence that the Frenchman and the German had secretly left.

When this had been done, and the boys had got themselves ready to go ashore and report, Captain Merceau told them how it had happened.  He had given orders, following the report made by Blake and his chums, that Secor and Labenstein should be kept under careful watch.  And this was to be done without allowing them to become aware of it.

“However, I very much doubt if this was the case,” the captain frankly admitted.  “They are such scoundrels themselves that they would naturally suspect others of suspecting them.  So they must have become aware of our plans, and then they made arrangements to elude the guard I set over them.”