I believe it was Red Skelton who said that to be a writer you have to be a close observer of human nature, but not so close that you start to hate everyone. P.D. James seems to frequently drift across the line into hating everybody. The men in James' world tend to be pompous, self-absorbed, preening narcissists, but they are almost nice compared to the women. The women are often petty, manipulative, mean-spirited and deliberately cruel.
Shroud for a Nightingale is about a series of murders at a small nursing school in rural England. It is about a group of women who work and live together in a rather small space and a veneer of niceness covers a lot of animosity. It is a solid mystery with a number of twists and misleads. Readers familiar with the conventions of the mystery genre may guess the solution, but I think James here is more interested in exploring the dark corners of her characters than with presenting a puzzle.