"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."