Once this gets moving, it's a good thriller with an interesting story that is well worth watching. It has a good cast, led by Basil Rathbone and Ann Harding. The last half of it builds up the suspense very nicely in leading up to a tense climax.
The story is a fairly straightforward one about a young woman who is swept away by a charming man, and then quickly marries him, but then begins to wonder if he is really what he seems to be. The first part is rather slow in setting everything up (the Agatha Christie story on which the play and movie are based is much more economical, and just as suspenseful), but stick with it, because the last part is more than worth waiting for. It squeezes quite a bit out of the possibilities that the situation offers, and you'll definitely want to find out what happens.