Ace Chinese detective Chan is back on the case and this one is regarded by most as one of the best in the entire Detective Chan series.The opera star Gravelle suffers amnesia. He is a recent escapee from an insane asylum, accused of murdering fellow performers (his wife and her lover). Included in the movie is the opera "Carnival", composed for the picture by Oscar Levant. Generally, when a horror star appears in a mystery movie they turns out to be an obvious red herring. I'm not going to say whether Karloff is one or not but will say that the movie does take the care not to make him an obvious one and in fact, the movie seems to take quite a bit of care all around; it looks like a lot of work went into the opera sequences, and the characters are a little more fleshed out than they usually are. Karloff's definitely is, and his presence is definitely a highlight of the movie, as are Warner Oland's (in the title role, of course) and William Demarest's, who makes several appearances as a police detective. The presence of Karloff definitely inspired a bit of the horror touches at the beginning of the movie, and there is an honourary reference to FRANKENSTEIN that seems to que into nearly every Karloff event or film he made during this time period. Also there's a quite amusing bit where the City Det.(William Demarest) tries to pick out Chan's son Lee (Keye Luke) from among a number of Asian knights in shining armor just off stage. A++++!