(I'm reading The Mystery of Dr Fu-Manchu or actually the American edition which was published under the title The Insidious Dr Fu-Manchu. Later in the series Fu-Manchu loses the hyphen and becomes Fu Manchu, in line with twentieth century romanisation of Chinese words and names. This hasn't happened yet; as Chapter Twenty Seven opens our heroes have just managed to escape Fu-Manchu and are stranded on the bank of the Thames, or conceivably a tributary but probably not.)
Smith is unhappy. "Pray God the river has that yellow Satan. I would sacrifice a year of my life to see his rat's body on the end of a grappling-iron!" He doesn't like Fu-Manchu.
They talk to Karamaneh who reveals that Fu-Manchu brought seven dacoits to England with him. Only one (probably) was still unaccounted for. As previously suspected he used the Thames as a highway, having several boats including at least one sea-going vessel, which she is unable to describe but believes has already left for China.
They meet with James Weymouth, the brother of Inspector Weymouth "four and a half miles S.S.E. of St. Paul's" in a "quaint little cottage, with its rustic garden, shadowed by the tall trees which had so lined the village street before motor 'buses were... a spot as peaceful and secluded as any in broad England."* They tell him all they can and Smith expands on his ignorance**.
Then Mr Weymouth tells them a story; Inspector Weymouth's wife, Mary had been thought to be having delusions; "for the last three nights poor John's*** widow has cried out at the same time—half-past two—that someone was knocking on the door." He was often late back from the yard before his disappearance. But then last night Weymouth's wife also heard it.
Petrie has other things on his mind. "Karamaneh laid her hand upon mine, in a quaint, childish fashion peculiarly her own. Her hand was cold, but its touch thrilled me. For Karamaneh was not a child, but a rarely beautiful girl—a pearl of the East such as many a monarch has fought for." Yes yes. If you like her so much why don't you marry her?
* Contrasting this idea of peaceful rural England with the horrors brought out of China by Fu-Manchu of course. Four and a half miles SSE of St Paul's is Forest Hill or Lewisham maybe.
** "Dr. Fu-Manchu was the ultimate expression of Chinese cunning; a phenomenon such as occurs but once in many generations. He was a superman of incredible genius, who, had he willed, could have revolutionized science. There is a superstition in some parts of China according to which, under certain peculiar conditions (one of which is proximity to a deserted burial-ground) an evil spirit of incredible age may enter unto the body of a new-born infant. All my efforts thus far have not availed me to trace the genealogy of the man called Dr. Fu-Manchu. Even Karamaneh cannot help me in this. But I have sometimes thought that he was a member of a certain very old Kiangsu family—and that the peculiar conditions I have mentioned prevailed at his birth!" So he's literally possessed by a demon? Interesting theory Smith.
*** John's brother is named James? Siblings with the same initial? What, is this the 1500s when they only had ten names?