I thought this was one of the better movies of its type I have watched on Amazon Instant Video. (By "its type," I mean "previously unknown to me, B picture, and oldish.")
I thought the mystery elements -- the unraveling of "who done it" and the clearing of the innocent party -- were well-plotted and interesting. And since that's the main part of the movie, that meant the movie was interesting for me. The drama and fighting and capturing-the-criminal parts were exciting.
I have seen Peter Haddon in another movie, and I like him. He has a rather fey, abstracted persona (if I know what "fey" means * ), and he gives people the impression he's a fool -- perhaps intentionally, like Zorro, or the Scarlet Pimpernel, or maybe like Peter Falk as Colombo. Being taken for a dummy works to his advantage. Anyway, I liked him as Lord Peter Wimsey. Others may differ.
All in all, I liked the whole tone of the movie, the interplay between various characters, and the whole package. A pretty good old mystery.
* I just looked up "fey." It means "giving an impression of vague unworldliness" -- that's Haddon's persona, all right. Kind of like Charles Butterworth, or maybe Roland Young.