“H-u-m!” said Carpenter thoughtfully, retrieving the paper he had just swept into the drawer. “How are we to work it, Mr. Marston?”
“As allies,” Marston replied. “I’m perfectly willing to let you have the book and everything in it, if you will let me have a copy of the letter. I’m confident that the key-word is here; I’m equally confident that the letter does not involve, either directly or indirectly, the United States. I understand that the letter is in the cipher of the Blocked-Out Square; in this book there are two pages and more of key-words to this Square, the last dozen or so of which are added in writing. If the letter is in that cipher, we should have no particular difficulty in finding the key-word. I would suggest, however, that we first try the last word on the list—maybe we won’t have to go any farther.”
“Very well,” said Carpenter, briskly.
The advantage was all with him. If Marston thought the letter was only a line and that he could 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—à l’aube du jour, I think it is ... yes, à 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 à 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. À 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.