Death of a Gentle Lady by M.C. Beaton

Mrs Gentle has fooled everyone into thinking she is as sweet as she sounds - Gentle by name and gentle by nature. But local constable Hamish Macbeth isn't fooled. He believes this little old lady is actually quite sly and vicious, but he's in a minority of one. Or is he?
When Mrs Gentle dies under unusual circumstances the villagers of Lochdubh are shocked and outraged. Chief Detective Inspector Blair suspects that members of her family may be involved but Hamish thinks there's much more to the story - and is willing to get rough to solve the riddle of Mrs Gentle's mysterious demise.