Oh dear. The problem with this film is the source material. Originally a screenplay for which its author Ivor Novello could find no takers, he was persuaded by his friend, actress Constance Collier, to turn it into a stage play. They collaborated on the adaptation under a pseudonym, and the result was a big hit in 1924; a successful film version followed, again with Novello in the lead, in 1925, and there were sequels in 1926 and 1928. (The critics did not care for any of its incarnations.) But by the time this sound remake came along in 1937, the whole thing was distinctly old hat. A never-never land Parisian underworld in which a dashing jewel thief is torn between an innocent girl entrusted to his care by her criminal father and a society woman slumming for her own amusement may have worked onstage thanks to the power of Novello's personality, and in silent film where the absence of spoken dialogue had already established a never-never land in which various improbabilities and implausibilities might be swallowed. However, a sound film is a different matter. The melodramatic clichés come thick and fast, and there isn't much anyone can do to disguise their familiarity and predictability.
The Rat's morality is curiously conservative (the original versions wouldn't have landed so successfully if it hadn't have been): although initially mean and short-tempered, he comes to worship René Ray's worshipful ingenue; considers the cocottes he normally associates with (and from whom he must previously chosen his sexual partners) as 'dirty'; and during a final argument with the society lady whose lover he has become, he snarls, 'At least I do not live off women.' O-kay... I mean, he sneaks into their apartments in the middle of the night and steals their jewellery, but I suppose that doesn't count...?
The film is only 72 minutes, but feels longer, never a good sign. There are only two reasons to see it: the performances of Anton Walbrook and Ruth Chatterton, both markedly superior to their surroundings. Mary Clare is also good fun as the duplicitous procuress, Mere Colline. By the by, if the then eighteen-year-old Betty Marsden of later Round the Horne fame is in this, as the IMDb says, she is not playing Chatterton's maid: that performer is a woman in late middle age.