“This envelope, however, is not French; it’s English,” Carpenter said instantly. “See! a saltire within an orle is the private water-mark of Sergeant & Co. I likely can tell you more after careful examination in my workshop.”
“How about the message itself?” Harleston asked.
“It is the Vigenèrie cipher, that’s reasonably certain; and, as you are aware, Mr. Harleston, the Vigenèrie is practically impossible of solution without the key-word. It is the one cipher that needs no code-book, nor anything else that can be lost or stolen—the code-word can be carried in one’s mind. We used it in the De la Porte affair, you will remember. Indeed, just because of its simplicity it is used more generally by every nation than any other cipher.”
“I thought that you might be able to work it out,” said Harleston. “You can do it if any one on earth can.”
“I can do some things, Mr. Harleston,” smiled Carpenter deprecatingly, “but I’m not omniscient. For instance: What language is the key-word—French, Italian, Spanish, English? The message is written on French paper, enclosed in an English envelope.—However, the facts you have may clear up that phase of the matter.”
“Here are the facts, as I know them,” said Harleston. Carpenter leaned back in his chair, closed his eyes, and listened.
“The message is, I should confidently say, written in English or French, with the chances much in favour of the latter,” he said, when Harleston had concluded. “Everyone concerned is English or American; the men who descended upon you so peculiarly and foolishly, and who showed their inexperience in every move, were Americans, I take it, as was also the woman who telephoned you. Moreover, she is fighting them.”
“Then your idea is that the United States is not concerned in the matter?” the Secretary asked.
“Not directly, yet it may be very much concerned in the result. We will know more about it after Mr. Harleston has had his interview with the lady.”
“That’s so!” the Secretary reflected. “We shall trust you, Harleston, to find out something definite from her. Keep me advised if anything turns up. It seems peculiar, and it may be only a personal matter and not an affaire d’état. At all events, you’ve a pleasant interview before you.”