Then a doubt arose in my mind.  Was it Bing?  Had I not made a mistake?  How could a smooth-shaven Dane with blond hair transform himself into a swarthy Russian with the beard of a Cossack?  There was, it is true, no change in the eyes or in the round head—­in the whiteness and width of the forehead, or the breadth of the shoulders.  All these I went over one by one as I watched him every now and then lean across the table and speak to some of the distinguished guests that surrounded him.  The thing which puzzled me was his grave, sedate demeanor, dignified, almost austere at times.  A man, I thought, might grow a beard and dye it, but how could he grow a different set of manners, how smother his jollity, how wipe out his spontaneous buoyancy?

No, it was not Bing!  It was only my stupid self.  I was always ready to find the mysterious and unnatural.  I turned to the guest next me.

“Do you know who that man is on the dais,” I asked; “the one all black and white, with the big beard?”

“Yes, one of the Prince’s suite; some jaw-breaking name with an ‘-usski’ on the end of it.  He brought him with him; looks like a bull pup chewing a muff, doesn’t he?”

I smiled at the comparison, but I was still in doubt.

When the banquet broke up I hurried out ahead of the others and posted myself at the top of the staircase leading down to the side door of the street.  The Prince’s carriage—­an ordinary cab—­was ordered to this door to escape the crowd and to avoid any delay.  This I learned from my old friend Alcorn of the Central Office, who was in charge of the detectives at the dinner, and who in answer to my request said: 

“Certainly I’ll let you through.  Come alone, and don’t speak to me as you go by.  I’ll say you’re one of us.  The crowd thinks he’s going out by the other door, and you can get pretty close to him.”

The Prince came first, wrapped in furs—­the black-bearded Russian at his side in overcoat, silk hat and white gloves.  The Ambassador and the others had bidden them good-night at the top of the staircase.

Under Alcorn’s direction I had placed myself just inside the street door where I could slip out behind the Prince and his black-bearded companion.  As a last resort I determined to walk straight up to him and say:  “You haven’t forgotten me, Mr. Bing, have you?” If I had changed so as to need proof of my identity Alcorn would furnish it.  Whatever his answer, his voice would solve my mystery.

He walked down the stairs with an easy, swinging movement, keeping a little behind the Prince; waited until Alcorn had opened the street door and with a nod of thanks followed Polinski out into the night.  Once outside I shrank back into the shadow of the doorway and held my breath to catch his first spoken word—­to the coachman—­to the Prince—­to any one who came in his way.

At this moment a man in a slouch hat and poorly dressed, a light cane under his arm, evidently a tramp, hurried across the street to hold the cab door.  I edged nearer, straining my ears.