I read the book on a phone screen, courtesy of Project Gutenberg.
Unlike some readers in “Agatha Christie: 100 Years of Poirot and Miss Marple”, I didn’t try hard to work out the puzzle. It felt early on that many of the clues were just too specific to the time and place: they rely on technologies (letters; chemists’ vials) and a society (class divide) that I don’t have an intuition for.
This is not a criticism. I enjoyed the quaintness of the atmosphere: the isolated country house; the fact that the brothers, John and Lawrence, decided to stop practising their professions to live as country squires; and the coroner’s inquest and jury trial, with realistic procedures and evidence.
Anyway the denouement was just as surprising and enjoyable, even when I didn’t try hard to puzzle it out.
PS It is surprising that a family solicitor could double-up as a Coroner: wonder if this really happened.