I stepped over to the door, where a constable stood on duty.  
"You observed a tall Eastern gentleman in the room a while ago, officer?"
 
"I did, sir."
 
"How long is he gone?"
 
The man started and began to peer about anxiously.
 
"That's a funny thing, sir," he said. "I was keeping my eyes specially upon him. I noticed him hovering around while Mr. Mostyn was speaking; but although I could have sworn he hadn't passed out, he's gone!"
 
"You didn't notice his departure, then?"
 
"I'm sorry to say I didn't, sir."
 
The man clearly was perplexed, but I found small matter for wonder in the episode. I had more than suspected the stranger to be a spy of Hassan's, and members of that strange company were elusive as will-o'-the-wisps.
 
Bristol, at the far end of the room, was signalling to me. I walked back and joined him.
 
"Come over here," he said, in a low voice, "and pretend to examine these things."
 
He glanced significantly to his left. Following the glance, my eyes fell upon the lean American; he was peering into the receptacle which held the holy slipper.
 
Bristol led me across the room, and we both faced the wall and bent over a glass case. Some yellow newspaper cuttings describing its contents hung above it, and these we pretended to read.
 
"Did you notice that man I glanced at?"
 
"Yes."
 
"Well, that's Earl Dexter, the first crook in America! Ssh! Only goes in on very big things. We had word at the Yard he was in town; but we can't touch him—we can only keep our eyes on him. He usually travels openly and in his own name, but this time he seems to have slipped over quietly. He always dresses t............