“To persuasion, no; to exchange, yes.  Our agreement is that if I provide the key-word, he will provide the letter in question.  At ten o’clock this morning the trick is to be turned.”

“And if the translation concerns the United States, he simply would turn the key upon you and hold you prisoner until the matter is cleared up.”

“One must take some risks,” Marston observed.

She nodded slightly.

“Which of these do you fancy is the key-word?” she asked.

“We shall try them in turn, beginning with the last:  a l’aube du jour.  I’ve a hunch that we’ll end there.”

“And that you’ll go into temporary confinement?” she smiled.

“My hunch stops with the key-word!” he smiled back.

“Your hunch as to the key-word is partially correct,” she replied slowly, “but it does not, however, reach quite to the last conclusion.  I may not explain now, Marston.  Do you go to the meeting, with the code-book as your only exhibit.  It should be indisputable proof of your good faith, and our honest belief that the letter does not concern the United States.  Moreover, you run no danger of imprisonment, for you’ll not effect a translation.  But you must obtain a copy of the letter; it’s but a fair exchange for the French code, you know; and you’re permitted—­nay you’re authorized, in the interest of the service—­to allow Carpenter to copy the book if he will give you the letter to copy.  Furthermore, you may proceed leisurely in the process; there is no particular haste; while they are occupied with the letter matter, there is apt to be less activity along other lines.  Only get a copy of the letter; I have the key-word.”

“You have the key-word!” Marston exclaimed.

She nodded.  “I’m quite sure of it; and the code-book confirms me.  It is up to you to procure the letter; I’ll do the rest, if any rest is necessary.  We may be headed for Europe by evening, Marston; in which event, the cipher letter is of no consequence to us.”

“You’ll be glad to get back to Paris?” he asked.

“I shall, indeed—­won’t you?”

“I’m quite content anywhere, so long as I am working with you,” he answered.  It was much as a faithful dog would wag his tail and snuggle up for a pat of the hand.

She smiled straight into his eyes—­a frank, appreciative smile, as though an intimate camaraderie existed between them, and would never be violated by either.  She would have been in danger had she smiled that way at some men; they would not have remained quiescent.  And a little more aggression by Marston might have been more conducive for success—­less of the faithful dog and more of the independent subordinate and the equal human.  As it was, he was only a plaything.

“Now, my friend, if you’re done you may go,” she said briskly.  “I must dress, and you’re rather de trop at such a time, however much you may be welcome at another.  And, Marston, don’t miss the copy of the letter; I’ll expect you with it at seven; we’ll make the translation together, either here or on the train to New York.  You’re to accompany me, you know.  I’ve an appointment at one, and another at four, but I’ll be here at seven.  If I’m detained, wait.”