“The man she spoke to,” hissed Smith.  “We must see him!  We must have him!”

He pulled the mat aside and stepped out into the anteroom.  It was empty.  Down the passage he led, and we were almost come to the door of the big room when it was thrown open and a man came rapidly out, opened the street door before Smith could reach him, and was gone, slamming it fast.

I can swear that we were not four seconds behind him, but when we gained the street it was empty.  Our quarry had disappeared as if by magic.  A big car was just turning the corner towards Leicester Square.

“That is the girl,” rapped Smith; “but where in Heaven’s name is the man to whom she brought the message?  I would give a hundred pounds to know what business is afoot.  To think that we have had such an opportunity and have thrown it away!”

Angry and nonplused he stood at the corner, looking in the direction of the crowded thoroughfare into which the car had been driven, tugging at the lobe of his ear, as was his habit in such moments of perplexity, and sharply clicking his teeth together.  I, too, was very thoughtful.  Clews were few enough in those days of our war with that giant antagonist.  The mere thought that our trifling error of judgment tonight in tarrying a moment too long might mean the victory of Fu-Manchu, might mean the turning of the balance which a wise providence had adjusted between the white and yellow races, was appalling.

To Smith and me, who knew something of the secret influences at work to overthrow the Indian Empire, to place, it might be, the whole of Europe and America beneath an Eastern rule, it seemed that a great yellow hand was stretched out over London.  Doctor Fu-Manchu was a menace to the civilized world.  Yet his very existence remained unsuspected by the millions whose fate he sought to command.

“Into what dark scheme have we had a glimpse?” said Smith.  “What State secret is to be filched?  What faithful servant of the British Raj to be spirited away?  Upon whom now has Fu-Manchu set his death seal?”

“Karamaneh on this occasion may not have been acting as an emissary of the Doctor’s.”

“I feel assured that she was, Petrie.  Of the many whom this yellow cloud may at any moment envelop, to which one did her message refer?  The man’s instructions were urgent.  Witness his hasty departure.  Curse it!” He dashed his right clenched fist into the palm of his left hand.  “I never had a glimpse of his face, first to last.  To think of the hours I have spent in that place, in anticipation of just such a meeting—­only to bungle the opportunity when it arose!” Scarce heeding what course we followed, we had come now to Piccadilly Circus, and had walked out into the heart of the night’s traffic.  I just dragged Smith aside in time to save him from the off-front wheel of a big Mercedes.  Then the traffic was blocked, and we found ourselves dangerously penned in amidst the press of vehicles.