W. Scott Darling wrote the screenplay for this film (1939) and changed very little plot-wise when he wrote the one for the Charlie Chan movie "The Chinese Ring" (1947). Both were an adaptation of his story for the 1931 film "Murder at Midnight."
I find it interesting that another Mr. Wong film, 1939's "The Mystery of Mr. Wong," contains some elements from "Murder at Midnight," including the playlet acted during a game of charades. Mr. Wong correctly guesses the mystery being enacted as "Murder Comes at Midnight."

https://archive.org/details/The_Chinese_Ring

This is to answer jonfrum's question... They use the exact same script... there are very few changes.

This was made 8 or 9 years earlier than the Charlie Chan version. Boris Karloff is no more believable playing a wise far Easten private eye than I would be. In the Charlie Chan version we get Roland Winters playing a man from the Far East. (Why is it that Charlie's wife and all of his kids are played by actors of Asian descent, but, Charlie never is?????) But, I digress...

The girl reporter in this version also played Peg Riley on "The Life of Riley"... she looks a little like Betty Grable in this Mr. Wong film.

In which Charlie Chan movie does a Chinese woman come to the Chan home to see Charlie, get murdered, and leave a note with only "Captain K" scrawled on it? Identical plotting to this movie.

I absolutely love his performance as mr. Wong in this series. Always staying calm, always showing that he is a superior mind but with so much understatement! Of course, although the make-up-artists did everything to make his face look asian mr. Karloff still looks like a european guy in disguise, but that is the same with every european actor (take the several Charlie Chan actors) in the time and maybe ever (or does Peter Sellers playing Fu Manchu look very asian?).

Grant Withers as his short tempered policeman friend who doesn´t understand anything also has to be mentioned. He plays this figure not as a simpleton but as a normally clever enough policeman who wants to do effective work and is not amused about cases which aslk too much of his sleuthing abilities.

By "Mort", I mean "le petit mort", if you know what I mean.

Watch her face as she dies. I believe we get a very personal insight. Wheeee!

Extra star for her death scene.

Mr. Wong in Chinatown. This is the first time I have seen Boris Karloff playing the Chinese detective Mr. Wong and it comes across as a very good performance. Highly entertaining mystery story. I would recommend it to everyone.

He played the oriental sleuth five times: Mr Wong, detective, the mystery of Mr Wong, Mr Wong in Chinatown, The Fatal Hour and Doomed to Die. The series was dumped when the Chan Mysteries came over from 20th Cent. Fox starring Sydney Toler.