“But, Smith, what is the motive of the Call?” I continued.

“Partly religious,” he explained, “and partly to wake the victims!  You are perhaps going to ask me how Dr. Fu-Manchu has obtained power over such people as phansigars?  I can only reply that Dr. Fu-Manchu has secret knowledge of which, so far, we know absolutely nothing; but, despite all, at last I begin to score.”

“You do,” I agreed; “but your victory took you near to death.”

“I owe my life to you, Petrie,” he said.  “Once to your strength of arm, and once to—­”

“Don’t speak of her, Smith,” I interrupted. 
“Dr. Fu-Manchu may have discovered the part she played! 
In which event—­”

“God help her!”

CHAPTER XVI

Upon the following day we were afoot again, and shortly at handgrips with the enemy.  In retrospect, that restless time offers a chaotic prospect, with no peaceful spot amid its turmoils.

All that was reposeful in nature seemed to have become an irony and a mockery to us—­who knew how an evil demigod had his sacrificial altars amid our sweetest groves.  This idea ruled strongly in my mind upon that soft autumnal day.

“The net is closing in,” said Nayland Smith.

“Let us hope upon a big catch,” I replied, with a laugh.

Beyond where the Thames tided slumberously seaward showed the roofs of Royal Windsor, the castle towers showing through the autumn haze.  The peace of beautiful Thames-side was about us.

This was one of the few tangible clews upon which thus far we had chanced; but at last it seemed indeed that we were narrowing the resources of that enemy of the white race who was writing his name over England in characters of blood.  To capture Dr. Fu-Manchu we did not hope; but at least there was every promise of destroying one of the enemy’s strongholds.

We had circled upon the map a tract of country cut by the Thames, with Windsor for its center.  Within that circle was the house from which miraculously we had escaped—­a house used by the most highly organized group in the history of criminology.  So much we knew.  Even if we found the house, and this was likely enough, to find it vacated by Fu-Manchu and his mysterious servants we were prepared.  But it would be a base destroyed.

We were working upon a methodical plan, and although our cooperators were invisible, these numbered no fewer than twelve—­all of them experienced men.  Thus far we had drawn blank, but the place for which Smith and I were making now came clearly into view:  an old mansion situated in extensive walled grounds.  Leaving the river behind us, we turned sharply to the right along a lane flanked by a high wall.  On an open patch of ground, as we passed, I noted a gypsy caravan.  An old woman was seated on the steps, her wrinkled face bent, her chin resting in the palm of her hand.