I suppose my growing perplexity was plainly visible, for Smith suddenly burst out with his short, boyish laugh.

“Oh!  I told you it was a strange business,” he cried.

“Is he mad?”

Nayland Smith’s gaiety left him; he became suddenly stern and grim.

“Either mad, Petrie, stark raving mad, or the savior of the Indian Empire—­perhaps of all Western civilization.  Listen.  Sir Gregory Hale, whom I know slightly and who honors me, apparently, with a belief that I am the only man in Europe worthy of his confidence, resigned his appointment at Peking some time ago, and set out upon a private expedition to the Mongolian frontier with the avowed intention of visiting some place in the Gobi Desert.  From the time that he actually crossed the frontier he disappeared for nearly six months, to reappear again suddenly and dramatically in London.  He buried himself in this hotel, refusing all visitors and only advising the authorities of his return by telephone.  He demanded that I should be sent to see him; and—­despite his eccentric methods—­so great is the Chief’s faith in Sir Gregory’s knowledge of matters Far Eastern, that behold, here I am.”

He broke off abruptly and sat in an attitude of tense listening.  Then—­

“Do you hear anything, Petrie?” he rapped.

“A sort of tapping?” I inquired, listening intently myself the while.

Smith nodded his head rapidly.

We both listened for some time, Smith with his head bent slightly forward and his pipe held in his hands; I with my gaze upon the bolted door.  A faint mist still hung in the room, and once I thought I detected a slight sound from the bedroom beyond, which was in darkness.  Smith noted me turn my head, and for a moment the pair of us stared into the gap of the doorway.  But the silence was complete.

“You have told me neither much nor little, Smith,” I said, resuming for some reason, in a hushed voice.  “Who or what is this Si-Fan at whose existence you hint?”

Nayland Smith smiled grimly.

“Possibly the real and hitherto unsolved riddle of Tibet, Petrie,” he replied—­“a mystery concealed from the world behind the veil of Lamaism.”  He stood up abruptly, glancing at a scrap of paper which he took from his pocket—­“Suite Number 14a,” he said.  “Come along!  We have not a moment to waste.  Let us make our presence known to Sir Gregory—­ the man who has dared to raise that veil.”

CHAPTER II

THE MAN WITH THE LIMP

“Lock the door!” said Smith significantly, as we stepped into the corridor.

I did so and had turned to join my friend when, to the accompaniment of a sort of hysterical muttering, a door further along, and on the opposite side of the corridor, was suddenly thrown open, and a man whose face showed ghastly white in the light of the solitary lamp beyond, literally hurled himself out.  He perceived Smith and myself immediately.  Throwing one glance back over his shoulder he came tottering forward to meet us.