The movie is well enough to stand alone so you do not need to be aware of the earlier "Shadow".
Now do not go comparing this to the radio show as that is apples and oranges.
Lamont Cranston/The Shadow (Kane Richmond) promises to marry his secretary, Margo Lane (Barbara Read) that knows how to type with two fingers. That is unless a case shows up. You guessed it a case shows up in the nick of time.
The case is full of mysteries. Some obvious and some a bit more complex. For a cheap movie the more complex "What it is all about?" and "How did they do it murder?" are quite good.
For some reason, probably because it is a formula in detective movies, they had to have over the top comic relief in the form of a taxi driver/Shadow assistant.
Overlooking the not so bright chief of police and the comic relief, the program is worth watching.