“Who will forestall us?” I asked in bewilderment.

“The biggest villain in Europe, Asia, or Africa!” cried my companion.  “I have wasted precious time to-day.  I might have known.”  He drummed irritably upon his knees.  “The place we have just left is a sort of club, you understand, Knox, and Hakim is the proprietor or host as well as being an old gentleman of importance and authority in the Moslem world.  I told him of my suspicions—­which step I should have taken earlier—­and they were instantly confirmed.  My man was there—­recognized me—­and bolted!  He’ll forestall us.”

“But my dear fellow,” I said patiently—­“who is this man, and what has he to do with the Deepbrow case?”

“He is the blackest scoundrel breathing!” answered Harley bitterly.  “As to what he has to do with the case—­why did he bolt?  At any rate, I know where to find him now—­and we may not be too late after all.”

“But who and what is this man?”

“He is Ali of Cairo!  As to what he is—­you will soon learn.”

IV

THE HOUSE BY THE RIVER

On quitting the singular Oriental club, Harley had first raced off to a public telephone, where he had spoken for some time—­as I now divined—­to Scotland Yard.  For when we presently arrived at the headquarters of the Metropolitan Police, I was surprised to find Inspector Wessex awaiting us.  Leaning out of the cab window: 

“Yes?” called Harley excitedly.  “Was I right?”

“You were, Mr. Harley,” answered Wessex, who seemed to be no less excited than my companion.  “I got the man’s reply an hour ago.”

“I knew it!” said Harley shortly.  “Get in, Wessex; we haven’t a minute to waste.”

The Inspector joined us in the cab, having first given instructions to the chauffeur.  As we set out once more: 

“You have had very little time to make the necessary arrangements,” continued my friend.

“Time enough,” replied Wessex.  “They will not be expecting us.”

“I’m not so sure of it.  One of the biggest villains in the civilized world recognized me three minutes before I called you up and then made good his escape.  However, there is at least a fighting chance.”

Little more was said from that moment until the end of the drive, both my companions seeming to be consumed by an intense eagerness to reach our destination.  At last the cab drew up in a deserted street.  I had rather lost my bearings; but I knew that we were once more somewhere in the Chinatown area, and: 

“Follow us until we get into the house,” Harley said to Inspector Wessex, “and wait out of sight.  If you hear me blow this whistle, bring up the men you have posted—­as quick as you like!  But make it your particular business to see that no one gets out!”

Into a pitch-dark yard we turned, and I felt a shudder of apprehension upon observing that it was the entrance to a wharf.  Dully gleaming in the moonlight, the Thames, that grave of many a ghastly secret, flowed beneath us.  Emerging from the shadow of the archway, we paused before a door in the wall on our left.