He smiled as he asked the question, and Miss Falconer smiled back at him.  Getting to her feet, she ran her fingers across the oak panel over his head, where for centuries a huntsman had been riding across a forest glade and blowing his horn.  The bundle of his hunting-knife protruded just a little; and as the girl pressed it, the panel glided silently open, revealing a space, square and dark and cobwebby.

Something was lying there, a thin, wafer-like packet of papers, the papers for which the Firefly of France had shed his blood.  She held them up in triumph.  But the duke was still smiling faintly.  He thrust one hand into his shirt and drew out a duplicate package, which he raised for us to see.

“Behold!” he said.  “They are copies.  All that I sketched that night near Ranceville, all that I wrote—­I did not once, but twice.  These I carried openly, to be found if I were captured.  But those you hold went hidden in the sole of my boot, which was hollowed for them, so that if I were taken and then escaped, they might go too!”

I had read of such devices, I remembered vaguely.  There was a story of a young French captain who had tried the trick in Champagne and succeeded with it, a rather famous exploit.  Then I thought of something else.  I got up slowly.

“You have two sets of papers?” I repeated.

“As you see, Monsieur.”

“Then I’ll take one of them,” said I.

Miss Falconer was looking at me in a puzzled fashion.  As for the duke, his brows drew together; his figure straightened; the cool glint grew in his eyes.

“Monsieur,” he stated somewhat icily, “such things as these are not souvenirs.  When they leave my possession they will go to the supreme command.”

“Certainly,” I agreed, unruffled.  “That will do admirably for the first package; but about the second—­no doubt Miss Falconer told you that we have German guests downstairs?  Perhaps she forgot to mention the leader’s name, though.  It is Franz von Blenheim.  And I don’t care to have him break down the door and burst in on us, on her specially; I would rather, all things considered, interview him in the hall.”

The Firefly’s face had altered at the name of the secret agent; he was now regarding me with intentness, but without a frown.  As for Miss Falconer, the trouble in her eyes was growing.  I should have to be careful.  Accordingly I summoned a debonair manner as I went on.

“If you’ll allow me,” I said, “I will take the papers down to him.  He won’t know that they are copies; he will snatch at them, glad of the chance.  And since he is in a hurry, he probably won’t stop to parley.  He will simply be off at top speed, and leave us safe.

“Of course, that is the one unpleasant feature of the affair, his going.”  At this point I glanced in a casual manner at the Duke of Raincy-la-Tour.  “It seems a pity to let him walk off scot-free, to plan more trouble for France; but that is past praying for.  I could hardly hope to stop him, except by a miracle.  If there is one, I’ll be on hand.”