After Warner Oland died, Sidney Toler took over the role of Charlie Chan. Oland brought a natural dignity to the role that made Charlie seem like a beloved, rotund uncle. Toler inherited scripts that required him to be gruff and uncompromising, rather than charming. The films were now produced at Monogram which didn't want to spend much money.
The Shanghai Cobra was filmed on a B budget but the script made an attempt to retain some of the better elements of the Oland movies. For example, I've always been a sucker for the "gee whiz" science in the Charlie Chan movies. The Shanghai Cobra is filled with cutting edge technology for its day from radium used in diagnostic work to a juke box that operates in part by television.
Cobra also added two humorous sidekicks, number three son Tommy (played by Benson Fong) and driver Birmingham Brown (portrayed by Mantan Moreland). Fong and Moreland play their roles in a more restrained way that Keye Luke and Stepin Fetchit did in the Oland films, and I think the restraint works well.
The story involves an escaped murderer who had killed a man in China by using cobra venom. When bank employees in the U.S. start dying from cobra venom as well, it's obvious that the same man may be involved. There's a problem though; the convicted murderer was badly burned and may have changed his appearance through plastic surgery. Only Charlie Chan may be able to recognize him.
The plot is very complex and will definitely challenge you to identify the murderer. I didn't detect any early clues to point out who it was. There's plenty of misdirection though to keep you guessing in all directions.
The strength of the film is its noir style which takes good advantage of subterranean adventures, secret passages, dark nights, lurking strangers, and drenching rain.
Don't expect this to be your favorite Charlie Chan film, but I think you'll have fun.