Disguised as humble Chinese hatter 'Fu Yuen', Charlie Chan assists the Secret Service way down in Panama, close to that so very important, narrow and vulnerable pathway between North and South America: the Panama Canal. And there are indications that there will be great danger for the US Fleet that is bound to pass through the Canal the next day: the dangerous international spy known only as "Ryner" probably is on the spot and planning something catastrophic - connected with anything from rats infected with bubonic plague to containers filled with nitroglycerin...!
Charlie very soon closes in on Ryner: he must have been on board the small airplane that takes passengers across the Canal, because one of his colleagues, who was also on the plane, dies right in Charlie's shop while they're discussing the case from a poisoned cigarette - but his cigarettes had been perfectly alright before he and the other passengers boarded the plane... And so we've got a shady night club owner, a young European fugitive singer without a passport, a strange scientist, an elderly lady teacher, an Egyptian who owns a tobacco shop - but Ryner's VERY clever, so Charlie (aided by son Jimmy even down in Panama - because while the cruise ship he was working on was stopping near the Canal, he took some photos of the forbidden military zone and ended up in jail...) has got to employ ALL his wits and cunningness in order to uncover him and save the US Fleet...
Another very nice piece of mystery entertainment, murder mixed with espionage this time - a GREAT challenge for fans who like to follow the story and find out the culprit even before the detective does; because in this case, for those who pay attention, it IS possible! Besides that, the Latin American atmosphere is very nice (it was hugely popular at the time), and the cast is great, so the movie flows very smoothly - but not without some sudden shock effects in between, of course... A great B movie classic, VERY worth watching.
