"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.

"Pa.s.s 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.