The story so far:
I raved about Greenshaw’s Folly (The Beeb episode of Agatha Christie’s Marple) particularly about the extravagant inclusion of country house mystery tropes, and then I pondered the absence of a secret door, during which I brought up Ronald Knox’ Ten Commandments of Detective Fiction. an alt site
#5 on Knox’ decalogue is a curious one: No Chinaman must figure in the story. What’s with the Asian hate?
Fortunately, in the many places where Knox’s list is spelled out, this is the one for which context is most often provided (which belies that WTF is a FAQ). The point of this rule is not racist in itself, but reveals racist trends during the golden age of mystery fiction. In this case, the yellow peril Wikipedia was in full force.
Dr. Fu Manchu was the stereotypical Chinese mastermind with sword-and-kung-fu-slinging mooks, drug-enhanced mysticsm and bio-chemical weapons and the occasional poisonous beastie. The early movies featuring him are regarded as super-racist, and Fu Manchu is the iconic representation of the yellow peril. There were previous examples of mysterious Chinese (opium) den-lords, but before or after, they looked like the fiendish doctor.
At some point, the Chinaman as culprit became as cliché as pernicious butlers. (Butlers have their own rule in Willard Huntington Wright’s Twenty Rules, in #11. A servant must not be chosen by the author as the culprit.)
Of course, Knox’ rules are more guidelines than actual commandments (as are Wright’s for that matter). Plenty of writers would include Chinamen (or butlers) in mystery stories to satisfactory effect, sometimes to specifically defy the notion that they should not. Earl Derr Biggers created Charlie Chan as a counter to the yellow peril stereotype, modeling the sleuth from Honolulu police officers Biggers knew in life.
Agatha Christie’s approach was to pull such characters into the foreground, giving them personalities and names so that they presented as clearly fair game as killers or victims. Applied to our practitioners of ancient Chinese mysticsm, you don’t keep the mysterious Chinaman mysterious for long, but give him visible mannerisms so that he can join in the party, and so it is with any other exotic, strange or well-traveled guest who has joined the cozy.
This serves as an early example of the Chimamanda Adichie rule (that I am so fond of raising). The way to escape stereotypes of a given sort is to portray many characters of that sort with a sweeping range of features. When dealing with a singular in a country house mystery, divorce that person’s traits and mannerisms from the stereotype. The housekeeper complains about being overworked, but that’s because she’s covering for the deceased butler not because gripes are expected from a housekeeper.
In the meantime Fu Manchu got a way-better moustache than Hitler did.
Image is not a Chinaman. Boris Karloff played Dr. Fu Manchu in the early movies. This one is from The Mask of Dr. Fu Manchu.