IT was with my mind in a condition of unique perplexity that I hurried with Nayland Smith into the cab which waited and dashed off through the streets in which the busy life of London just stirred into being. I suppose I need not say that I could penetrate no farther into this, Fu-Manchu's latest plot, than the drugging of Norris West with hashish? Of his having been so drugged with Indian hemp—that is, converted temporarily into a maniac—would have been evident to any medical man who had heard his statement and noted the distressing after-effects which conclusively pointed to Indian hemp poisoning. Knowing something of the Chinese doctor's powers, I could understand that he might have extracted from West the secret of the combination by sheer force of will whilst the American was under the influence of the drug. But I could not understand how Fu-Manchu had gained access to locked chambers on the third story of a building.  
"Smith," I said, "those bird tracks on the window-sill—they furnish the key to a mystery which is puzzling me."
 
"They do," said Smith, glancing impatiently at his watch. "Consult your memories of Dr. Fu-Manchu's habits—especially your memories of his pets."
 
I reviewed in my mind the creatures gruesome and terrible which surrounded the Chinaman—the scorpions, the bacteria, the noxious things which were the weapons wherewith he visited death upon whomsoever opposed the establishment of a potential Yellow Empire. But no one of them could account for the imprints upon the dust of West's window-sill.
 
"You puzzle me, Smith," I confessed. "There is much in this extraordinary case that puzzles me. I can think of nothing to account for the marks."
 
"Have you thought of Fu-Manchu's marmoset?" asked Smith.
 
"The monkey!" I cried.
 
"They were the footprints of a small ape," my friend continued. "For a moment I was deceived as you were, and believed them to be the tracks of a large bird; but I have seen the footprints of apes before now, and a marmoset, though an American variety, I believe, is not unlike some of the apes of Burma."
 
"I am still in the dark," I said.
 
"It is pure hypothesis," continued Smith, "but here is the theory—in lieu of a better one it covers the facts. The marmoset—and it is contrary from the character of Fu-Manchu to keep any creature for mere amusement—is trained to perform certain duties.
 
"You observed the waterspout running up beside the window; you observed the iron bar intended to prevent a window-cleaner from falling out? For an ape the climb from the court below to the sill above was a simple one. He carried a cord, probably attached to his body. He climbed on to the sill, over the bar, and climbed down again. By means of this cord a rope was pulled up over the bar, by means of the rope one of those ladders of silk and bamboo. One of the Doctor's servants ascended—probably to ascertain if the hashish had acted successfully. That was the yellow dream-face which West saw bending over him. Then followed the Doctor, and to his giant will the drugged brain of West was a pliant instrument which he bent to his own ends. The court would be deserted at that hour of the night, and, in any event, directly after the ascent the ladder probably was pulled up, only to be lowered again when West had revealed the secret of his own safe and Fu-Manchu had secured the plans. The reclosing of the safe and the removing of the hashish tabloids, leaving no clew beyond the delirious ravings of a drug slave—for so anyone unacquainted with the East must have construed West's story—is particularly characteristic. His own tabloids were returned, of course. The sparing of his life alone is a refinement of art which points to a past master."
 
"Karamaneh was the decoy again?" I said shortly.
 
"Certainly. Hers was the task to ascertain West's habits and to substitute the tabloids. She it was who waited in the luxurious car—infinitely less likely to attract attention at that hour in that place than a modest taxi—and received the stolen plans. She did her work well.
 
"Poor Karamaneh; she had no alternative! I said I would have given a hundred pounds for a sight of the messenger's face—the man to whom she handed them. I would give a thousand now!"
 
"ANDAMAN—SECOND," I said. "What did she mean?"
 
"Then it has not dawned upon you?" cried Smith excitedly, as the cab turned into the station. "The ANDAMAN, of............