“I will promise both,” she said.  “Who attends you to-night?”

“My Aide, Colonel Moore.”

“Suppose, then, we make it a party of eight and ask Lady Helen, the Countess de Relde, Mademoiselle d’Essolde and the American Ambassador.”

“Charming!” I exclaimed; “charming!”

“And what hour will Your Highness be served?” she asked.

“At whatever hour Madame la Marquise fixes.”

“Say, one o’clock, then—­in the blue breakfast room; it is quiet and retired.”

I bowed again over her hand and was withdrawing, when the Marquise stopped me.

“Would not Your Highness like to know some of the Masques?” she asked.

“Very much, indeed,” said I.

“Then you will find a chair in the recess behind the curtains, yonder—­and, when you are tired, there is a door, which slides without noise, opening into a private corridor leading to the Garden. Comprenez vous, Monsieur le Prince?”

I laughed.  “Perfectly,” said I.  “And I may have Colonel Moore with me?  There will be many faces I shall not know.”

“He is without?” she asked.

“Yes—­and costumed somewhat like myself.”

She touched a bell; I held up my mask.

“Admit the gentleman in black velvet, like Monsieur,” she ordered.

“Goodness!” she exclaimed, when Moore entered.

“Puzzle,” said I.  “Pick the Archduke.”

“Impossible—­and, if you two go around together, some of my guests will think they are getting double vision very early in the evening.”

From the recess, we could see all that entered and hear every word said.  And it struck me how very eloquent it was of the character of the Marquise de Vierle that she should, deliberately, provide a concealed audience while she greeted—­alone—­every man and woman of Dornlitz Society.  I must admit I rather enjoyed the experience—­though I very rarely guessed the face behind the mask.  It is astonishing how effectively an unusual costume disguises even those we know well.

Suddenly, the Marquis entered hurriedly.

“Do you know, Claire,” he said, “that the American Archduke is here to-night?”

Instantly I laid my hand on the sliding door.  It was time for us to be going.  And the door refused to move.  I looked at Moore, who shrugged his shoulders.  I could imagine the smile his mask concealed.  But the Marquise met the situation with a laugh.

“I do indeed—­and I rather fancy you will find His Highness in yonder recess,” she said.

I parted the curtains and stepped out—­and Colonel Moore beside me.

“Madame la Marquise has taken pity on the stranger,” I said; “and has given him an opportunity to recognize his friends.”

If the diplomat were surprised, no one would have guessed it—­except that his bow was more than usually low.

“It is a great privilege, my dear Prince, if we can be of any use to you,” he said.