In addition to being a first-rate mystery novel, and, I think, one of the best of Earl Derr Biggers' books featuring Charlie Chan, the movie version of The Black Camel is the oldest surviving movie about Charlie Chan. I haven't seen it, but I believe there are copies available on DVD (used, alas!) and it does turn up on oldies channels occasionally.
The movie features Warner Oland as Charlie Chan. It also features actor Bela Lugosi as Tarneverro, the mysterious and sinister fortune-teller who plays a critical role in the story. The Black Camel was made and released in 1931 - the same year that Lugosi had starred in the title role of the movie of Dracula. His name was certainly known to movie audiences, and it appears he brought that air of mystery and terror to the role of Tarneverro. If you are reading the original book of The Black Camel, try to keep Lugosi's face and powerful personality in mind as you read about the character and imagine his interaction with Warner Oland's Charlie Chan. Looking back over the distance of 82 years, it would seem to have been a brilliant casting choice.