“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 the Oriental Navigation Company’s line, leaves Tilbury with the next tide for China ports.  Our man is a second-class passenger.  I am wiring to delay her departure, and the special should get us to the docks inside of forty minutes.”