I'm not quite sure why this melodrama failed to work for me; it has a starry cast (Conrad Veidt, Cedric Hardwicke) and (so far as can be discerned beneath the worn print and large-size Czech subtitles) lavish sets and high production values. The BFI's programme notes comment that "unfortunately, the screenplay was rather weak", and it's certainly very slow-moving. For a melodrama, very little actually happens -- which is frankly rather an anticlimax -- and this can be laid at least partially at the door of a screenplay that drags every confrontation scene out beyond the obvious; there is an entire abortive consultation between Dr Isaacson and Mona at the beginning which so far as the plot is concerned subsequently appears to serve no purpose at all, other than perhaps establishing the character as a manipulative vamp and Isaacson as being resistant to her charms.
For me Cedric Hardwicke was the highlight of the film; when he was off-screen for the central third of the plot I found myself quite literally falling asleep, a tendency that miraculously evaporated again as soon as the good doctor showed up -- although this could be due to the fact that his arrival is the trigger for further plot happenings... It was not, so far as I can tell, that Hardwicke's performance was especially superior to those of his colleagues (John Stuart gives a nicely-judged portrayal of the infatuated but not unintelligent Nigel), but simply that he was the only one who, for whatever reason, actually engaged me in the proceedings.
Conrad Veidt's role, however, didn't work for me at all; he is excellent elsewhere (as the lead in Powell & Pressburger's "The Spy in Black" for instance), but the part of a cruel and apparently irresistible Egyptian gives him very little to work with. The entire plot more or less pivots around Mona's attraction to him and willingness to do anything to enjoy his attentions, but I simply couldn't see the mesmeric attraction in the character, while he doesn't really get much to do.
There are some good moments, such as the unspoken revelation of just why Mona did marry Nigel in the first place, or Nigel's reluctant leap of understanding as he infers the truth from his friend's explanation of his illness, but they are generally vastly over-extended, rather than being cut off at the point of greatest impact. Characters like Lady Harwich or the enthusiastic Ibrahim seem to wander in and out of the action and then get forgotten about; the effect is not one of lively background characterisation, but rather of arbitrary exposition. The surviving print contains various blips in the soundtrack at the end of scenes where material is evidently missing, so it's hard to tell whether the original version was more evenly developed; but given that the film's longueurs are excessive as it stands, it seems unlikely that a lengthier version than this 85-minute print would be much of a general improvement.
I'm not quite clear if the story is supposed to be Mona's tragedy or a morality play about the evils of infidelity; either way, the ending is unsatisfying. But the real trouble was that the attempt to create a "mystical and decadent" atmosphere of mutual lust -- despite shots of Veidt fondling dancing girls' breasts -- was simply soporifically dull.
