"Yes, it was a good job you did, I don't think."

"Wait a minute, though," said Jack. "If it were a trap, it would be plainly evident we didn't know what we were talking about. That should be enough to let us out."

"Unless they believe we smelled a mouse and acted accordingly," returned Frank.

"Oh, well," said Jack, "there is no use worrying about it. We'll have to take what comes and that's all there is about it. Now, I'm going to rest a bit. When they come in, wake me up."

He leaned back in his chair and closed his eyes; and in the meantime Frank continued to turn events over in his mind.

Half an hour later Lord Hastings, the man who had led the party that captured the boys, a figure attired in the uniform of a colonel of infantry, and several others entered the room. The uniformed man Frank immediately took to be Colonel Masterson, and he was right. Frank nudged Jack and the latter opened his eyes. Then both boys got to their feet.

"So these are the German spies, eh?" said Colonel Masterson.

"That's not true," declared Frank hotly. "We are no more spies than you are."

"So?" said the colonel insinuatingly. "Then how does it happen you hold such friendly conversation with another man who is under suspicion?"

Frank's heart sank. So it had been a trap, after all.

"I can explain that, sir," said the boy, turning to Lord Hastings.

"I have no doubt of that," was the reply. "The question is, can you explain it satisfactorily?"

"Yes, sir, we can," interrupted Jack.

Here Colonel Masterson took a hand again. He spoke to Lord Hastings.

"What shall we do with them?" he asked.

"That, colonel, is for you to decide," was Lord Hastings' reply.

"Do you think it necessary to call a court martial?" continued the colonel.

"In view of the evidence we have, I should say not," returned Lord Hastings.

"And still," said Colonel Masterson, half to himself, "it seems to me that every man should be given a chance."

In the minds of the two boys now there was not the slightest doubt that they were in as perilous a situation as they had ever faced.

"Lord Hastings," said Jack quietly, "I assure you you are all mistaken. However, we shall protest our innocence no longer, for I see it would be useless."

And then the two lads were treated to one of the surprises of their lives. Lord Hastings' stern expression gave way to a smile, and he strode quickly toward them and extended a hand to each.

"Surely," he said, "you didn't think I doubted you."

The lads were too stunned to say a word.

"I just wanted to teach you a little lesson," continued Lord Hastings. "In the future, perhaps you will neither fall short nor go beyond your orders. I ordered you to Gravesend. You should not have gone beyond."

"But Davis, sir?" exclaimed Frank.

"As long as you were here, apparently prisoners," was the reply, "I simply used you to advantage. Davis is a German spy."

CHAPTER IV.

STRANGE WARFARE.

It was the following night.

Clad in heavy oilskins, Frank and Jack stood in the bow of the large, high-powered motorboat as it sped down the Thames in the darkness. Not a light was visible anywhere and it was impossible to see a yard ahead. But in spite of this, the boat fairly flew over the water; for the strong hand of Lord Hastings was on the wheel and there was not a spot in the river with which he was not familiar.

"Whew!" said Jack, as he turned about to shield his face from the icy spray. "This is what I call taking a long chance, if you ask me."

"I should say so," replied Frank, raising his voice to a shout to make himself heard above the sound of the whistling wind. "Wonder how long we are going to keep this up?"

"Don't know," responded Jack. "But I don't feel very comfortable. This is too fast for me."

"Particularly when you can't see where you are going," Frank agreed.

Both became silent and peered into the intense darkness ahead.

For possibly half an hour the motorboat continued its terrific speed; and then it slowed down abruptly. The two boys heard Lord Hastings call them. They felt their way to where he stood by the wheel, for it was impossible to see.

"Here," said their commander, "take this searchlight and flash it ahead. See if you can pick up anything."

He passed a small but powerful searchlight to Jack, who again moved to the bow.

Jack pressed the little button and a tiny but brilliant light flashed over the water before the boat. There was nothing in sight, so far as the boy could see.

"Nothing ahead, sir," he reported to Lord Hastings.

"Guess we had better remain about here, anyhow," muttered Lord Hastings, half to himself.

Although the lads had no idea of the nature of their present mission, they had asked no questions of their commander. They knew he would tell them whatever he deemed necessary when the time was ripe; and until that time they were satisfied to await whatever might transpire.

But one thing the boys had noticed which had given them much food for thought. In the prow was mounted a small but heavy gun, and a second one of the same size loomed up formidably astern. Plainly they were there for a purpose, and Frank and Jack both realized that there was serious work ahead of them.

Lord Hastings himself had examined both guns carefully and announced that they were in first-class condition.

"All ready for use," he had said.

And now, although neither lad knew it, the time was fast approaching when they were to be greatly needed.

Several times in the course of the next hour Lord Hastings ordered Jack to see what he could pick up ahead; but each time the result had been the same. There was nothing to disturb the calm peacefulness of the night.

And then they were spared the need of another look, for there suddenly loomed up less than a hundred yards ahead a dull-glowing white light.

"To the forward gun, Mr. Templeton," ordered Lord Hastings, thus, for the first time on this mission, falling into old aboard-ship terms.

Jack sprang forward.

"Man the gun astern."

Frank obeyed this command with alacrity.

Then the two lads awaited developments.

Apparently the craft ahead had not discovered the presence of the motorboat containing Lord Hastings, Jack, Frank, and a crew of four men; neither did the distance between the two boats seem to diminish. The two were not approaching each other.

"Twenty-five knots," came Lord Hastings' command, and the little craft seemed to leap ahead.

The light ahead drew closer.

"Train your gun on her, Mr. Templeton," ordered Lord Hastings, "and if I give the command, fire to sink her."

This command was needless, for Jack had already gauged the range and trained the gun. Nevertheless he replied:

"Yes, sir."

The pursuers now had approached within fifty yards of their quarry, and still not a sound save an occasional order from Lord Hastings had broken the stillness of the night. There had been nothing to indicate that the other boat was even occupied, save the sudden appearance of the light aboard.

But now, as the pursuers crept even closer, there came a sudden startled exclamation from ahead; and at the same moment the light disappeared.

"Fire!" cried Lord Hastings.

"Boom!"

Jack had fired the gun.

There was another startled exclamation from ahead.

"Did you hit her?" asked Lord Hastings.

"Think so, sir," replied Jack. "Don't see how I could have missed at that distance."

"We'll cruise about a bit and see," said Lord Hastings.

He gave the command and the motorboat slowed down.

For half an hour the little craft circled about, but there was no trace of the other boat. All aboard flashed searchlights about the water, and the larger light in the bow was turned on, casting a bright ray over the