The Spanish Cape Mystery (1935)
A few notable points about this old-fashioned whodunit:
1. It's the first film adaptation of an Ellery Queen novel.
2. Ellery Queen is already so famous a character that the other characters all know him as the "famous detective." We even see somebody reading The Adventures of Ellery Queen.
3. Despite this fact, the leading lady (the delightfully named Helen Twelvetrees) gets her name before the title, and Donald Cook as the hero gets his after it.
4. The first ten minutes or so of the film is irrelevant to the plot, as we see Ellery help his police inspector solve a jewel robbery.
5. There isn't a whole lot of 1930's comic relief, which is a good thing, although Ellery is portrayed as something of a wiseguy.
6. The setting -- a mansion on an isolated cliff somewhere on the California coast -- is interesting, with some nice views of the ocean. (Admittedly, most of the film is set inside the house, with lots of talking.)
7. This almost becomes a body count film, with no less than four murders.
8. The whodunit aspect of the plot is fairly interesting. I was able to figure out who the killer was likely to be, but the odd aspects of the case -- why the murderer removed the first victim's clothing, leaving him only in a pair of bathing trunks and a cape -- were a puzzle to me until Ellery explained it all.
Overall, a decent way to pass the time if you're in the mood of this sort of thing.