From Doon with Death
by Ruth Rendell
This is the first Inspector Wexford novel, and while it isn't as fully formed as some of her later books, it's still a good one. A dull housewife is found in the woods, violently murdered in an apparent crime of passion. Though at first few claim to remember her, the investigation turns up a series of strange relationships with the victim.
Even once you've figured out the trick, (which you will; it may have been missable in 1964, but it's a pretty easy one now) Rendell has one decent red herring left. You'll still figure it out by the end, but Rendell always makes for a good story along the way.
The second Wexford novel, Sins of the Fathers, strikes me as a degree of magnitude better; it has a fairly unconventional ending for a mystery novel, and some squirmy philosophical questions in the mix. Rendell, who started off writing good, solid stories, was apparently a quick study in the art of mystery novels.