The best book on music I've ever read is "The Classical Style: Haydn, Mozart and Beethoven", by Charles Rosen. (Read it, it's fascinating.) One of Rosen's claims is that the classical style was the offspring of two impulses: the desire to surprise, and the desire to be formally perfect, to sound "right". In the decades before Haydn's maturity there were composers who startled and composers who satisfied; Haydn was the first to startle and satisfy in the same breath.
Detective story writers have the same ideal as classical composers. The solution must surprise us; yet the "shape" of the story, to those who know the solution, must be beautiful. And, as in music, it's hard to surprise and satisfy at once. If you must go one way or the other, much better to satisfy. One can see the denouement of a Thorndyke story by R. Austin Freeman a mile off, but it's always perfectly crafted, and that is enough. Too many modern detective stories startle us by having the murderer turn out to be one of a dozen characters when it could so easily have been one of the other eleven and nobody would have particularly cared because there's little beauty in the story whoever it turns out to be. But Agatha Christie ... not for nothing is she called "classical". Her solutions are almost always surprising - she may have been better at misdirection than anyone else who ever lived - but they always, in a way that's hard to describe, make perfect dramatic sense. -Okay, so she's not the world's best mystery WRITER. But I often think she attracts undue criticism because she so obviously writes less well than she plots, while the literary defects of writers who can't plot either pass unnoticed.
For all these reasons I'm surprised there aren't more first-rate films based on her works. (I can understand, though, why "The Mousetrap" has never been filmed.) Looking through the IMDb list of twenty-eight cinematic Christies, I'm surprised how many of the ones I've seen fall short of their potential. And twenty-eight isn't really, when you think about it, that many, especially when so many of them are remakes of earlier ones.
Still, most are worth watching, and this particular one is excellent. Faithful to the play, it has the usual finely crafted, classical, Agatha Christie twist. Wilder made it at a moment in his career when he could do no wrong. It must have taken him all of two seconds to decide that Charles Laughton would make the perfect Sir Wilfrid; then, perhaps, another fifteen minutes to settle on Marlene Dietrich as the title character. Just as "Double Indemnity" is set in a black-and-white California, "Witness" is set in a black-and-white England - it makes me wonder if it's a mistake filming Agatha Christie in colour. You'll enjoy this, trust me.
