"I have this officer's word," he said, indicating the boys' captor, "that you were captured under suspicious circumstances. I thought I knew you—both of you—but it may be that I have been mistaken. Stranger things have happened than for a man to sell out to the enemy. I cannot interfere with the officer in the performance of his duty."

"But, sir——" began Jack.

Now the officer interrupted.

"You know them?" he asked of Lord Hastings.

"I thought I did," was the reply. "It would seem that I have been mistaken."

"I should say it does," said the officer. "Certainly they were making their way down the river for no good purpose."

"I am afraid I must agree with you. However, I shall not interfere. You may do as you think best with them."

"Very good, sir." The officer motioned the boys to precede him to the stairs at the far end of the room. "Up with you," he commanded.

Frank hung back.

"Prod him up a bit there, men," instructed the officer.

A second man advanced and pushed his revolver against Frank's ribs.

"Move along," he commanded gruffly.

"Now look here——" began the lad, but Jack interrupted him.

"Come, Frank, don't be a fool," he said.

He led the way up the stairs, and Frank, still grumbling, followed. At the top of the steps the boys were marched into a small room. The door closed behind them and a key turned in the lock.

"Now," said Frank, turning to his friend, "what is the meaning of all this?"

"You know just as much about it as I do," was the reply.

"But a word from Lord Hastings would have settled all this."

"But he didn't give it, did he?"

"No, he didn't; and that's what seems so strange. It looks to me as though we are in for a peck of trouble."

"Say! you heard what Lord Hastings said about 'selling out.' Do you think he believes us guilty of such a thing?"

"It's hard to tell what a man believes in times like these. Men have been stood up against a wall and shot on less evidence. You remember taking a shot at the other boat, don't you?"

"Yes, but——"

"'Buts' won't help us any, I'm afraid. I can't account for Lord Hastings' actions, but you may be sure he has good reasons for whatever he does. It may even be true that he suspects us."

"By George! I don't believe that," exclaimed Frank.

"It doesn't seem possible; but still you can't tell."

"But what are we going to do?"

"Do? There is nothing we can do. We'll have to stay here until they decide what to do with us. There is nothing else to do."

The boys kept up their conversation for some time, and the more they talked the more they became convinced that their plight was more serious than they had at first supposed. It seemed very plain to them now that Lord Hastings must believe in their guilt and that he would not raise a finger in their behalf.

It was after midnight and the boys were still talking when the key again turned in the lock of the heavy door. It swung inward and their captor entered.

"Down stairs," he said briefly, motioning them to march down ahead of him.

The lads obeyed this order.

There was no one in the room below; and the lads sat down before the fireplace to await whatever might transpire.

"There will be no use trying to escape," said their captor. "The place is surrounded. You would be shot down like dogs. Now just be as comfortable as you can. I have business elsewhere."

He wheeled about quickly and disappeared through the door and the lads heard him lock it after him.

"Well, why are we allowed to sit here in solitary glory?" asked Frank.

"Ask me something easy," returned Jack. "We're here; that's all I know about it. However, I don't imagine we shall be here alone very long."

And he was right, although the first corner could not possibly have been in his mind, nor the nature of his coming.

Jack's attention was attracted toward the window by a slight squeaky sound. The lad glanced toward it, but no second sound followed immediately.

"Sounded like some one at the window," he said to Frank.

"I didn't hear anything," said the latter.

A moment later the noise came again. Jack sat up straight in his chair.

"Hear that?" he asked.

Frank nodded affirmatively.

"Some one there, all right," he agreed.

He made as though to rise, but Jack stayed him.

"Wait and see what happens," he said softly.

Both leaned back in their chairs and seemed to pay no further heed to the window. But without looking each became aware that the window was being raised softly, and clear across the room they could hear the breathing of a man. A foot sounded on the floor and at that moment both boys sprang to their feet and faced the intruder.

Before either could speak, the newcomer laid a finger to his lips in a sign for silence and came toward them.

"Quick!" he whispered, when he was close to them. "Tell me what you have learned. This may be your only chance!"

Frank and Jack stepped back in astonishment.

"Tell you what?" demanded the latter.

"What you have learned," repeated the man. "About the vanishing submarines. What has happened to them?"

Noticing the apparently puzzled looks on the faces of the two boys, the man smiled slightly and thrust a hand into his inside vest pocket.

"I see," he whispered. "You want to be sure it is all right. Here. Look!" he exhibited a small card. "My number. Thirty-two. See it?"

Jack's quick mind took in the situation on the instant.

"But you are no German," he protested.

"No, I'm English. Name of Davis. But I am in the game for what it's worth, the same as you are."

"I see," said Frank. "And you have been sent after our information?"

"Yes; and I shall have to hurry. We may be interrupted at any moment."

"We haven't had time to jot down anything," said Jack, "but we'll tell you what we have learned."

He whispered for some moments and Davis nodded understandingly. At last the boy ceased his whispering.

"And that's all you know?" asked Davis.

"Absolutely all," replied Jack, and added to himself, "and a whole lot more than I know, for that matter."

"Then," said Davis, "you believe that if we can get to the mouth of the Thames we can learn the whole secret?"

"That is my opinion," said Jack.

"Good; then I'll pass the word along. Good-bye."

Davis moved toward the window and a moment later disappeared on the outside.

"Now," said Frank to Jack, "just what did you tell that fellow? I couldn't hear all that whispering."

"Well," replied Jack, "I told him we had learned very little; but that the secret of the whole affair was at the mouth of the Thames; that that was where we were heading for when we were captured."

"And did you give him some kind of a hint as to the nature of the mystery?"

Jack smiled.

"Well, yes," he said. "I told him he would find some queer explosives there and a large number of swift torpedo boat destroyers, equipped with submarine nets. I told him that these made nightly raids into the Channel and the North Sea and thus disposed of the German submarines."

"And he believed it?"

"He seemed to. But that was the best I could do on short notice and knowing no more than I do of the matter."

"Well, it wasn't so bad," grinned Frank.

"I flatter myself that it could have been worse," returned Jack modestly.

They fell into a long silence, which was suddenly broken by Frank, who exclaimed anxiously:

"Say! Do you suppose that could have been a trap?"

"Trap?" repeated Jack. "What do you mean?"

"I mean, do you think Lord Hastings or some of the other British officers sent that man here simply to get evidence against us?"

"By Jove!" exclaimed Jack. "I never thought of that. Whew! Maybe I have gotten us into worse trouble than ever."

"If it was a trap, I guess you have," returned Frank glumly.