Like it or not, mystery fiction is a very plot-driven genre. This is not to say that plot trumps everything - characterization, writing, setting have their importance as well - but plotting is more crucial to mystery fiction than it is to, say, sci-fi or western; one might even say that it is a defining feature of it. How comes then that modern critics tend to focus on a mystery novel's literary virtues, while either downplaying or ignoring outright plot?
An obvious answer is that many contemporary mysteries tend to be stronger in the literary department than the plotting one, not necessarily because their authors are weak plotters but simply because their interests are elsewhere. And yet "literary" mysteries with strong plots get the same treatment. A good example is Thomas H. Cook who is regularly (and rightly) praised for the elegance of his prose and the depth and richness of his characterization but almost never for his plots even though he is arguably the finest plotter in American crime fiction since Margaret Millar (with whom he has a lot in common, but I'll leave that for another post) I do agree with critics that Instruments of the Night or Red Leaves are fascinating studies in character and tragedy, but they're also masterful exercises in bamboozling and their final twists are central to the books' effects.
One of the mistakes that dragged so much of "literary" fiction into the pit of irrelevance and self-indulgence was to discard plot as unimportant. It is thus worrying to see mystery critics follow in the same trap. A good plot, as any serious mystery buff knows, is a hard thing to find - and it should be celebrated rather than swept under the rug. The P-word is not a dirty word.