Oh, I used to be quite into Japrisot when I could read French fluently. A couple of his books were made into films, Un long dimanche de fiancailles really stuck with me, both the book and the film. The English title I think is A very long engagement. It's not exactly crime, it's about a woman with mild learning disabilities who falls in love with a man and he goes off to fight in WW1 and disappears, due to a brain injury causing amnesia. And the book is about trying to find him again, so it's like a mystery but it's not a whodunnit, it's looking for clues to find this guy. Really good characterisation and sense of place, I hadn't thought of the comparison with Mary Stewart.