“What are you going to do about the young woman?” Jack found a chance to whisper, as all hands gathered on the platform deck.

“I don’t believe I have actual authority to do anything,” Kimball returned, also in a whisper.  “But we have the drawings, and that writing, which may be a clever cipher.  With that I’m afraid we’ll have to remain content.”

A launch from the gunboat was in waiting.  In this the shore guests were taken back to land.  Hardly had the launch left the side of the submarine, when a cutter, also from the gunboat, put in alongside.  Two men in ordinary citizen’s dress clambered aboard.

“Lieutenant Commander Kimball?” inquired one of the pair.

“Yes,” acknowledged the naval officer.  “May we see you below, in the cabin of this boat.”

“No!” replied Kimball, sternly.

“Oh, as you please, of course,” smiled the one of the pair who had first spoken.  “Probably I am at fault, though, in not introducing my companion and myself.  My friend is Mr. Packwood; my name is Trotter.  We are Secret Service men sent down here by the Secretary of the Navy, in answer to your dispatch.”

As Trotter spoke he threw back the lapel of his coat, displaying a badge.

“I have also some papers to show you, Mr. Kimball,” continued the Secret Service man.

“Oh, of course you may come below,” smiled the naval officer.  “And, Benson; I guess this business belongs to you, too.”

So Jack descended with the party, while the other submarine boys and Williamson remained on deck.

“You have, been bothered with spies, Captain?” asked Trotter, turning to young Benson, when they had reached the cabin table.

“Haven’t we, though!” muttered Jack.

“And even took one out with you on this last trip of yours,” laughed Mr. Trotter, producing from an inner pocket a book bound in black.

“Miss Peddensen, the Swedish young woman?” demanded Captain Jack.

“Here’s the one I mean,” replied Trotter, opening the book, which proved to be an album, and turning the pages over rapidly.  He pointed to a photograph.

“That’s Miss Peddensen,” cried Jack, looking up at Lieutenant Commander Kimball for confirmation.

“Well, Peddensen is one of the names she has used,” smiled Trotter.

“What foreign government does she serve?” demanded Benson.

Trotter shrugged his shoulders.

“Well, the Department has pretty good information that she has served England, France, Germany, Austria, Russia—­oh, these spies have no country!  They serve the fattest international purse!”

“Here is what we took from Miss Peddensen,” said Kimball, gravely, laying down on the table the sketchbook and the “composition.”

Taking up the latter, Mr. Trotter, after a glance declared: 

“This is written in a secret cipher, most likely.  Packwood, this comes in your peculiar line of work.  The sketches are easy enough to understand.  They are of the mechanisms displayed in this cabin.”