Agatha Christie's The Body in the Library
A few months ago, I watched a bunch of the Miss Marple mysteries on Hulu, and this one was my favorite (primarily because it involved Patsy from Absolutely Fabulous constantly bragging about how awesome her friend Miss Marple was, but also because it was just a cleverly told mystery), so I was interested to see the source material (which does differ in some large respects). And it was just as good--really well-plotted and with a hilariously dry narrative voice. I love how all the important police dudes are like "But what does Miss Marple think???" the whole time. Old ladies getting stuff done. Totally my jam. A/A-.