So, as in the first book of the series, the main character is a feckless American who is caught up in intrigue between China and Japan, and Mr. Moto pops in, sort of like a Deus Ex Machina
, perhaps, to fix things at the end.
In this case, the protagonist, Tom Nelson, is an American lawyer (from Boston, I believe), who has taken up life with the ex-pat community in Peking, and has more-or-less "gone native". He just slides through his life. "It doesn't matter, does it?" is his favorite and oft repeated phrase.
Tom gets involved with a beautiful young woman, Eleanor Joyce, who is in Peking to buy art antiquities for an American museum. She has a sort of Wernher von Braun approach to her work. Von Braun is known as the guy whose job was to get rockets into the air. Where they came down was not his concern (his original rockets, made for the Nazi's, were V2 rockets designed to blow up patches of London. Later the U.S. hired him to design ICBMs to blow up patches of the Soviet Union).
"Once the rockets are up,
who cares where they come down?
That's not my department,"
says Wernher von Braun
Eleanor's job is to buy art. Where the art comes from is not her concern. In this book, the art is being stolen by some Chinese brigands who hope to finance a rebellion. A British ex-major is helping broker the deal, but then ends up inconveniently murdered, just after Tom, and slightly later on, Eleanor have visited the major. So, they become implicated and are, perhaps, the next victims on the list.
A Japanese spy from a different government faction than Mr. Moto's is trying to foment unrest in China, the unrest being financed by the art deal. Mr. Moto's government faction, is trying to quell the unrest. They don't want further unpleasantness in China to be blamed on the Japanese. They think they can expand their empire via more subtle means, or something.
Whatever, there's lots of skullduggery, tight scrapes and so forth. Tom's paternalistic attitude toward Eleanor gets a bit wearying. She's the competent one in the bunch, but he thinks, by dint of his having a y-chromosome, that he is naturally meant to be the decider and the protector. I'm glad we've evolved, at least a little bit, from that 1930s nonsense.
Anyway, this is a quite good book. I don't know enough about 1930s Chinese culture to know if the setting is more-or-less appropriate. I'm guessing Marquand did enough research to make things a reasonably accurate reflection of the times, or at least the book's subset of those times.