Nayland Smith nodded his head.

“Exactly!” he snapped.

“Inspector Weymouth, here,” continued Fletcher, “has put me in possession of such facts as are known to him, and I believe that I have had the good fortune to chance upon a valuable one.”

“You interest me, Sergeant Fletcher,” said Smith.  “What is the nature of this clue?”

“I will tell you,” replied the other, and turned briskly upon his heel to face us.

He had a dark, clean-shaven face, rather sallow complexion, and deep-set, searching eyes.  There was decision in the square, cleft chin and strong character in the cleanly chiseled features.  His manner was alert.

“I have specialized in Chinese crime,” he said; “much of my time is spent amongst our Asiatic visitors.  I am fairly familiar with the Easterns who use the port of London, and I have a number of useful acquaintances among them.”

Nayland Smith nodded.  Beyond doubt Detective-sergeant Fletcher knew his business.

“To my lasting regret,” Fletcher continued, “I never met the late Dr. Fu-Manchu.  I understand, sir, that you believe him to have been a high official of this dangerous society?  However, I think we may get in touch with some other notabilities; for instance, I’m told that one of the people you’re looking for has been described as ’the man with the limp’?”

Smith, who had been about to relight his pipe, dropped the match on the carpet and set his foot upon it.  His eyes shone like steel.

“‘The man with the limp,’” he said, and slowly rose to his feet—­“what do you know of the man with the limp?”

Fletcher’s face flushed slightly; his words had proved more dramatic than he had anticipated.

“There’s a place down Shadwell way,” he replied, “of which, no doubt, you will have heard; it has no official title, but it is known to habitues as the Joy-Shop....”

Inspector Weymouth stood up, his burly figure towering over that of his slighter confrere.

“I don’t think you know John Ki’s, Mr. Smith,” he said.  “We keep all those places pretty well patrolled, and until this present business cropped up, John’s establishment had never given us any trouble.”

“What is this Joy-Shop?” I asked.

“A resort of shady characters, mostly Asiatics,” replied Weymouth.  “It’s a gambling-house, an unlicensed drinking-shop, and even worse—­ but it’s more use to us open than it would be shut.”

“It is one of my regular jobs to keep an eye on the visitors to the Joy-Shop,” continued Fletcher.  “I have many acquaintances who use the place.  Needless to add, they don’t know my real business!  Well, lately several of them have asked me if I know who the man is that hobbles about the place with two sticks.  Everybody seems to have heard him, but no one has seen him.”

Nayland Smith began to pace the floor restlessly.

“I have heard him myself,” added Fletcher, “but never managed to get so much as a glimpse of him.  When I learnt about this Si-Fan mystery, I realized that he might very possibly be the man for whom you’re looking—­and a golden opportunity has cropped up for you to visit the Joy-Shop, and, if our luck remains in, to get a peep behind the scenes.”