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.