"What is the meaning of Si-Fan?" asked Detective-sergeant Fletcher.  
He stood looking from the window at the prospect below; at the trees bordering the winding embankment; at the ancient monolith which for unnumbered ages had looked across desert sands to the Nile, and now looked down upon another river of many mysteries. The view seemed to absorb his attention. He spoke without turning his head.
 
Nayland Smith laughed shortly.
 
"The Si-Fan are the natives of Eastern Tibet," he replied.
 
"But the term has some other significance, sir?" said the detective; his words were more of an assertion than a query.
 
"It has," replied my friend grimly. "I believe it to be the name, or perhaps the sigil, of an extensive secret society with branches stretching out into every corner of the Orient."
 
We were silent for awhile. Inspector Weymouth, who sat in a chair near the window, glanced appreciatively at the back of his subordinate, who still stood looking out. Detective-sergeant Fletcher was one of Scotland Yard's coming men. He had information of the first importance to communicate, and Nayland Smith had delayed his departure upon an urgent errand in order to meet him.
 
"Your case to date, Mr. Smith," continued Fletcher, remaining with hands locked behind him, staring from the window, "reads something like this, I believe: A brass box, locked, contents unknown, has come into your possession. It stands now upon the table there. It was brought from Tibet by a man who evidently thought that it had something to do with the Si-Fan. He is dead, possibly by the agency of members of this group. No arrests have been made. You know that there are people here in London who are anxious to regain the box. You have theories respecting the identity of some of them, but there are practically no facts."
 
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 habitués as the Joy-Shop…."
 
Inspector Weymouth stood up, his burly figure towering over that of his slighter confrère.
 
"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."
 
"I am all attention," snapped Smith.
 
"A woman called Zarmi has recently put in an appearance at the Joy-Shop. Roughly speaking, she turned up at about the same time as the unseen man with the limp…."
 
Nayland Smith's eyes were blazing with suppressed excitement; he was pacing quickly up and down the floor, tugging at the lobe of his left ear.
 
"She is—different in some way from any other woman I have ever seen in the place. She's a Eurasian and good-looking, after a tigerish fashion. I have done my best"—he smiled slightly—"to get in her good books, and up to a point I've succeeded. I was there last night, and Zarmi asked me if I knew what she called a 'strong feller.'
 
"'These,' she informed me, contemptuously referring to the rest of the company, 'are poor weak Johnnies!'
 
"I had nothing definite in view at the time, for I had not then heard about your return to London, but I thought it might lead to something anyway, so I promised to bring a friend along to-night. I don't know what we're wanted to do, but …"
 
"Count on me!" snapped Smith. "I will leave all details to you and to Weymouth, and I will be at New Scotland Yard this evening in time to adopt a suitable disguise. Petrie"—he turned impetuously to me—"I fear I shall have to go without you; but I shall be in safe company, as you see, and doubtless Weymouth can find you a part in his portion of the evening's program."
 
He glanced at his watch.
 
"Ah! I must be off. If you will oblige me, Petrie, by putting the brass box into my smaller portmanteau, whilst I slip my coat on, perhaps Weymouth, on his way out, will be good enough to order a taxi. I shall venture to breathe again once our unpleasant charge is safely deposited in the bank vaults!"