I didn't quite finish this one before falling asleep last night, so I grabbed it and finished it this morning.
This is one of Christie's true standalones - one of those books containing none of her recurring characters. No Poirot or Marple, but also no Colonel Race, no Inspector Japp or Ariadne Oliver or Inspector Battle. It is set in the same geographic district as The Hound of the Baskervilles, and has some commonalities of plot.
The main character, Emily Trefusis, is a wonder of a girl. Smart and a self-starter, engaged to the hapless Jim, who ends up finding himself arrested for the murder of Colonel Trevelyan, his uncle. She reminds me of one of the characters in After the Funeral, Susan Banks - both Emily & Susan are capable young women engaged (in Emily's case) or married (in Susan's case) to feckless but handsome young men. They have no qualms about being the leader in the relationship, and I get the feeling that both of them are eyes-wide-open sorts of women who will make a success of themselves. Highly competent. Christie seems to have mixed emotions about these characters - both admiring them and, as well, deploring them a bit. Which makes me wonder about her self-image. I imagine that she was, herself, a highly capable young lady.
Anyway, I liked it. I liked Emily, even if I did think she was far too good for Jim. But she didn't, and that's what matters. Plus, I love books set on the moors.