Authorial manipulation and mismanagement in Muriel Spark's Memento Mori

We're all familiar with the cinematic device that Hitchcock call the McGuffin (sp?), a fact,clue, or object that sets the plot in motion and that over the course of the narrative diminishes in relevance until, b the end, we've pretty much forgotten what started everything rolling. Mission Unnecessary. That's what Muriel Spark does in Memento Mori - she begins the novel with a hang-up call to an elderly woman that could be interpreted either as a death threat or as a simple statement of fact: Remember, you will die soon (or words to that effect). It would be one thing if Spark left that element alone, but she keeps developing it over the course of the novel - others start getting similar threats, the police investigate, a distinguished retired detective offers his services, and so forth. And guess what (spoilers coming): She doesn't ever tell us who's making the calls. Just gives us some nonsense like: Death itself is calling. Hey, a novelist can do whatever she wants - but as this is clearly not a scifi or fantasy novel but an otherwise completely realistic drawing-room British drama, wealth elderly Brits squabbling about inheritances and past infidelities, the type that translates so well, usually, to TV screens - doesn't she owe us a little more on the payoff, can't she even make an effort? Compound this with the plot itself - which becomes a very complex web of accusations and guilty disavowals, of characters continually revising their wills - and the one will at the center of the story - which seemed to be destined to the elderly woman's caretaker - gets snatched up by an old literary lion who, everyone suddenly, had been secretly married to the late Lisa. But then - oh, surprise - we learn in the last chapter that the marriage was invalid because Lisa's first husband, presumed dead, was alive and is still alive in a mental hospital - so he inherits all the loot. This is even more manipulative and random than, say, Dickens at his worst. Despite all this authorial mismanagement, there are a few good scenes in this novel, in particular the inter-relationships of the elderly women in a hospital ward. We can see that Spark matured in her later writing and she learned to focus the story on smaller set of characters and a well-defined struggle for power - thinking her of her later and far more accomplished novel Prime of Miss Jean Brodie.