business. We must be cautious."

"Cautious!" repeated Frank. "We won't find that German being cautious."

"If we weren't cautious, it wouldn't do us any good if we did find him," argued Jack. "First thing you know we would be at the bottom."

Frank considered this point a moment.

"Guess you're right," he said at last.

"Swish!" went something at this moment, and, turning quickly, Frank saw a dark shape speeding away up the river.

"Hey! There went one the other way," he cried to Jack.

"That so?" replied Jack anxiously. "There is something up here, and I'm going to find out what it is."

He slowed down even more, and, striking a match, lighted the searchlight, which, until this moment, he had not deemed advisable.

As the light flashed over the water, the lad made out another small motorboat dead ahead, upon which signs of life became apparent. Jack saw figures gesticulating violently; then the boat headed directly for the one occupied by the two boys.

"Guns, Frank!" said Jack quietly. "They are coming at us."

"Leave it to me," replied Frank. "You run the boat. I'll do the rest."

"Don't shoot unless you have to," warned Jack.

Frank made no reply.

Jack kept the light full upon the approaching boat. He could see several oilskin-clad figures and that was all; and then came a hail from the oncoming boat.

"What do you want here?"

The query was in English. Jack answered the hail.

"What are you doing here yourself?" he demanded. "We are British officers. I command you to surrender."

"More likely German officers," was the response. "Heave to now. I'm coming aboard you."

"If you do you'll get a warm welcome," replied Jack.

He stopped the boat and drew his own revolvers.

"Stand back!" he cried, as the other boat came closer.

In the glint of the searchlight the men aboard the other boat made out the boys' uniforms. The boat slowed down and the men talked among themselves.

"They wear British uniforms," said one in a low voice.

"That's no sign they are English," said another.

"Tell 'em to give the countersign," said a third.

Another hail came from the boat.

"Pass the countersign," it said.

"I don't know any countersign," replied Jack, and would have said more, had not a voice from the other boat interrupted him.

"I thought not; hands up now or you are dead men. Quick!"

Jack made his decision in a moment. Much as he would have liked to fight it out, he determined upon a wiser course.

"Hands up, Frank," he said quietly. "They've got the drop on us."

He raised his hands in the air.

Not so Frank.

"They won't get me without a fight," declared the lad angrily, and, raising his voice, he cried:

"Come and get me, if you want me."

At the same moment he raised his revolver and fired.

"Here," cried Jack angrily, "don't be a fool. Give me that gun."

He seized Frank's wrist and wrenched the revolver from his grasp.

The latter turned on his chum angrily.

"What do you mean by that?" he demanded. "Have you turned coward, that you surrender to a couple of Germans without a fight?"

"I haven't turned crazy," replied Jack quietly. "They are too many for us; that's all."

The other boat came alongside now and an officer stepped aboard the boys' craft.

"Your weapons," he said in perfect English.

"Then please step aboard my boat. You shall be taken to Gravesend at once."

"Gravesend!" echoed Jack. "You couldn't take us to a better place. But if you are German, why should you take us there?"

"German," repeated the man. "You know we are English. You are the German spies."

"No such thing," declared Frank, taking a hand in things. "We are British officers and we thought you were German spies. That's why I fired at you. We thought you were here to learn the secret of the vanishing submarines."

"Frank!" cried Jack in warning, but it was too late.

"The vanishing submarines, eh?" repeated the stranger. "So you have given yourselves away. Who but a German spy would be here seeking word of the vanishing submarines?"

"But I tell you——" began Jack.

"Silence," thundered the officer. "You have betrayed yourselves, and that is enough. I give you my word you shall be shot in the morning."

"Oh, I guess not," replied Frank with a laugh. "I guess Lord Hastings will be able to get us out of this mess."

"Lord Hastings?"

"Why, yes, we happen to serve under him; that's all."

"Tell it to the marines," replied the man with sarcasm. "I am not asking you to admit anything, for I know enough now."

"Oh, all right," said Frank.

"Climb into my boat," ordered their captor.

The lads complied.

"Say," said Frank, "this is Lord Hastings' motorboat. He told us not to lose it. Tie it on behind and pull it along, will you?"

"We'll pull it along all right," replied their captor. "Now the best thing you fellows can do is to keep quiet."

The lads obeyed this gruff command, for they had nothing particular to talk about.

Half an hour later the motorboat docked at Gravesend and the boys were ordered to climb out, which they did, under the noses of their captors' weapons.

"Where to now?" asked Frank.

"Where I tell you," was the reply.

Jack was struck by a sudden thought.

"Will you tell me what time it is, sir?" he asked the leader of the party which surrounded them.

"As you ask in such a polite way, I shall do so," was the reply. "I wouldn't tell this other fellow anything. He's too smart." He produced his watch, and after a glance at it, said: "Five minutes to ten."

"By George!" exclaimed Jack. "And we were to meet Lord Hastings at the Lion Inn at 10 o'clock."

"I can promise you'll be at the Lion Inn at 10 o'clock," replied the leader of the capturing party, "but whether you will find Lord Hastings there I can't say."

"You mean you are taking us there?" asked Jack.

"Exactly."

"That's what I call luck," broke in Frank. "We'll be all right in a few moments now, Jack."

"You'll be all right till in the morning, I can guarantee that," growled their captor.

At the door of the inn he motioned them to enter ahead of him. They did so and the first person on whom their eyes rested was Lord Hastings.

"Well, I see you are on time——" the latter began, and then broke off as he saw the armed men behind them.

"Yes, sir, we are on time," replied Frank with a smile, "and we have brought company to see you, sir!"

CHAPTER III.

A LESSON.

Lord Hastings was on his feet by this time and advanced toward the two lads and their captors.

"What's the meaning of this?" he demanded of the man who appeared to be the leader.

"We caught these fellows scooting down the Thames in a high-power motorboat, sir," was the reply. "They were unable to give a satisfactory account of themselves and one of them took a shot at us. So we brought them here."

"Do you know who they are?" asked Lord Hastings, smiling a bit to himself.

"No, sir; but I would take them for a couple of German spies, sir."

"H-m-m," muttered Lord Hastings. He stroked his chin a moment and then asked: "And what do you intend to do with them?"

"Turn them over to Colonel Masterson, sir, who will return about midnight. He is stopping here, sir."

Lord Hastings seemed to consider the matter a few moments, and then, with a gesture, he turned on his heel, remarking:

"Well, I can't see that it is any of my business."

"Very good, sir," said the boys' captor.

Frank and Jack had remained quiet up to this time, but now the former took a step after his commander, exclaiming:

"Aren't you going to get us out of this, sir? You can explain that we have done no wrong."

Lord Hastings turned toward him.