Excellent psychological murder-motivations, not physical clues, solve this one.
Fine Miss Silver mystery, about village life disrupted by (surprise, surprise) annonymous letters.
POISON IN THE PEN by Patricia Wentworth is a classic English village whodunit. Featuring Miss Maud Silver, an English spinster who was a teacher but is now a "private enquiry agent". In this book, a friend who happens to be an Inspector for Scotland Yard asks her to discreetly visit a small village where a spate of nasty anonymous letters has resulted in a young woman's suicide. But that's not the end of the problems.
It's nicely plotted, and if there were clues lying about to be guessed I didn't guess them. You can't read it without comparing it to Agatha Christie (if someone had told me the plot without names, I'd have said "Miss Marple!"), but it holds its own very well. Miss Silver is apparently possessed of a magical ability to inspire confidences from everyone, pretty handy if you're a PI. Of course the attitudes come across as very quaint 60 years later, but you won't cringe at them.
There are some 30-odd Miss Silver books, but this one reads fine as a stand-alone; I expect they all do given when they were written.