As a film this is only so-so, although it does contain some extremely atmospheric compositions by "lighting expert" (as the credits call him) Brian Langley. But in addition to early glimpses of Nigel Patrick (in his film debut) & Irene Handl it provides a meaty role for Mary Clare in the title role, probably inspired by RKO's Hildegarde Withers.
I don't recall a Mr Pym (just as I don't think the film tells us that her first name is 'Palmyra'). But Mrs Pym is refreshingly an actual Scotland Yard detective for once - albeit an extremely eccentric one constantly patronised by her colleagues - rather than yet another amateur sleuth; while Edward Lexy's Det-Inspector Shott, although always several steps behind Mrs Pym, is not the dunce James Gleason always was as the cop in the Hildegarde Withers films.