SILVER BLAZE was quite inappropriately retitled "MURDER AT THE BASKERVILLES" when it was released in the US in 1941. though it has nothing much to do with this great Sherlock Holmes story--other than adding the Henry Baskerville character for no apparent reason. Instead, the film is roughly Conan Doyle's "The Silver Blaze"--but with many changes--most notably the addition of Moriarty and Col. Sebastian Moran. Oddly, these characters (especially Moriarty) were included in many Holmes films even though in the books he was only a minor character (the same could be said of Inspector Lestrade). In reality, Moriarty appeared in just a few stories and was ultimately killed in a fight with Holmes mid-way through the series. Unfortunately, the addition of Moriarty didn't do much to bring excitement to the film and this master criminal seemed inexplicably involved in a very petty case that seems beneath his genius.
I really don't want to describe the plot--others have done so and IMDb has a summary. Instead, it's important to talk about the overall effort. The film was made by a "poverty row" studio (Astor Films) and sure bears the earmarks of such a cheap film. Many of the outdoor scenes are clearly sets--and not very good ones. The acting is okay, but combined with a rather dull script and music, it just seems to have no life. Now I am not necessarily blaming those who played Holmes and Watson. Holmes was much closer to the books than the flamboyant character played by Basil Rathbone and Ian Fleming managed to play a decent Watson--not a total idiot like he was in many films (though not in the books). While their performances were decent, they cannot hold a candle to the Granada Television series of the 1980s--the Jeremy Brett series was just perfect and the scripts stayed extremely close to the brilliant original stories.
So overall, this is a very watchable but jumbled film plot-wise. The acting is okay--not great but not bad, however the whole thing lacks energy. Worth seeing if you are a Holmes fan, but otherwise you'll probably find the whole thing a bit dull.