I read this after having burned through a number of other Sax Rohmer ebooks, and it wasn't my favorite at all; I much preferred his Fu Manchu novels.
The story is standard pulp fare -- detective, mysterious murder, dark secrets, enigmatic villain, beautiful ingenue, etc. So far, so good. Like other Rohmer books, there are some elements which presage the Indiana Jones movies (especially, here, Temple of Doom).
This particular pulp potboiler has several problems, though.
1) The writing is comically bad. The keynote might have been when the protagonist declares this the "biggest case of my career" when we have literally no idea who the villain might be, but there were many other sharp contenders (an honorable mention must go, for example, to "You are out after one of the big heads of the crook world").
2) the plotting is painfully predictable. When an elderly man visits the protagonist, announces he thinks people are trying to kill him, begs for assistance, and then decides to tell Our Hero about it all later that day, over dinner, instead of, you know, right then in his office like he came there to do. . .yeah. We all know about how long that guy's going to live (exactly long enough to choke out an Enigmatic Phrase over the soup). By itself, that kind of thing wouldn't be so bad, but, well, there's another problem:
3) The misogyny and racism. The best example of this work's misogyny might be this two-line exchange between the protagonist and the ingenue: ""Why do you insist on treating me like a child?"/"Perhaps because I enjoy doing so". The real kicker, though, is the books' casual racism; lines like "The manicurist incident indicated an inherent cruelty only possible in one of the Oriental race" are all too common, and whenever the heroes take an oath it's "on [their] honor as a white man," etc. On the one single occasion where a caucasian does something reprehensible, the narrator takes care to note "the prominence of upper jaw singularly reminiscent of the primitive Briton . . . utter stupidity and dogged courage are the outstanding characteristics of this type."
It's possible to defend that sort of thing by saying Rohmer was a creature of his era, but even at the time he was writing, Rohmer was decried for the rampant racism in his books; one of the later Fu Manchu novels, published shortly before WW2, features the protagonists attempting to save a Hitler analogue and thereby foil Fu Manchu's plot to prevent a world race war.
Regardless, though, for a modern reader, this kind of thing is fairly painful to read. In his Fu Manchu novels, it's worth working past the racism just to read the iconic descriptions of the Fu Manchu character. Here, though . . . well, there's no Fu Manchu here, and without that iconic character, what's left is just racist pulp. Skip this one, and grab the Fu Manchu series instead.