ld remember the letters used, he was in for a shock.
No man living could remember twenty spilled alphabets; and if he
attempted to make a copy it could easily be prevented. The Fifth
Secretary spread the paper on the table.

"Here is a copy of the cipher letter in question--we had it made large
for convenience," he explained. "The original is in the safe; you'll wish
to compare it with the copy, so we'll have it here."

He gave the necessary order; when the letter was brought he passed it to
Marston.

"I'll read the copy, if you'll hold the original," he said; and
proceeded to call off the letters with amazing rapidity. "Correct, isn't
it?" as he ended.

"Yes!" said Marston returning the original to Carpenter. He wanted in
every way to disarm suspicion; moreover, a copy could be made more
readily from a large typewritten edition than from the small, written
original. "Now for the code-book and the last key-word--_a l'aube du
jour_, I think it is ... yes, _a l'aube du jour_, it is," and he handed
the book across. "Shall we try it first, Mr. Carpenter?"

"By all means," said Carpenter. "Shall I set it down, or will you?"

One would never have imagined from his expression or his intonation that
he had already tried _a l'aube du jour_ for the key-word and failed;
nor that why he had failed he now knew. The book was right as to the
word, and the slip that Harleston had taken from Crenshaw's pocket-book
confirmed it. _A l'aube du jour_ was not the key-word but the key-word
was constructed from it by some arbitrary rule; and that rule was
susceptible of solution. After he was free of this fellow Marston, he
would solve the problem quickly enough. It was as sure as tomorrow. The
prescience was come.

"About twenty letters should be enough for experiment?" he suggested,
taking up a test card.

When he had written the key-word and the letters under it, he, scarcely
without reference to the Blocked-Out Square, wrote the translation.
Marston did the same, very much slower.

"It doesn't fit!" Marston announced. "You can't make anything out of
AGELUMTONZN, and so forth."

"I can't!" Carpenter smiled--and waited. Would Marston suggest the
transposed or elided word?

"I'm disappointed," Marston confessed, "I thought sure we had it. Let's
try the next key-word in the book."

They tried it, and the next, and all the rest. None of them translated
the letter.

It took more than an hour; at the end, as a full measure of goo