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.”