“Surely some arrests were made?”

“But there was no evidence!” cried Ryman.  “Every inch of the rat-burrow was searched.  The Chinese gentleman who posed as the proprietor of what he claimed to be a respectable lodging-house offered every facility to the police.  What could we do?”

“I take it that the place is being watched?”

“Certainly,” said Ryman.  “Both from the river and from the shore.  Oh! they are not there!  God knows where they are, but they are not there!”

I stood for a moment in silence, endeavoring to determine my course; then, telling Ryman that I hoped to see him later, I walked out slowly into the rain and mist, and nodding to the taxi-driver to proceed to our original destination, I re-entered the cab.

As we moved off, the lights of the River Police depot were swallowed up in the humid murk, and again I found myself being carried through the darkness of those narrow streets, which, like a maze, hold secret within their labyrinth mysteries as great, and at least as foul, as that of Pasiphae.

The marketing centers I had left far behind me; to my right stretched the broken range of riverside buildings, and beyond them flowed the Thames, a stream more heavily burdened with secrets than ever was Tiber or Tigris.  On my left, occasional flickering lights broke through the mist, for the most part the lights of taverns; and saving these rents in the veil, the darkness was punctuated with nothing but the faint and yellow luminance of the street lamps.

Ahead was a black mouth, which promised to swallow me up as it had swallowed up my friend.

In short, what with my lowered condition and consequent frame of mind, and what with the traditions, for me inseparable from that gloomy quarter of London, I was in the grip of a shadowy menace which at any moment might become tangible—­I perceived, in the most commonplace objects, the yellow hand of Dr. Fu-Manchu.

When the cab stopped in a place of utter darkness, I aroused myself with an effort, opened the door, and stepped out into the mud of a narrow lane.  A high brick wall frowned upon me from one side, and, dimly perceptible, there towered a smoke stack, beyond.  On my right uprose the side of a wharf building, shadowly, and some distance ahead, almost obscured by the drizzling rain, a solitary lamp flickered.  I turned up the collar of my raincoat, shivering, as much at the prospect as from physical chill.

“You will wait here,” I said to the man; and, feeling in my breast-pocket, I added:  “If you hear the note of a whistle, drive on and rejoin me.”

He listened attentively and with a certain eagerness.  I had selected him that night for the reason that he had driven Smith and myself on previous occasions and had proved himself a man of intelligence.  Transferring a Browning pistol from my hip-pocket to that of my raincoat, I trudged on into the mist.

The headlights of the taxi were swallowed up behind me, and just abreast of the street lamp I stood listening.