Baroness James knows how to write a good mystery. She's got the eye for detail, the understanding of human psychology, and the ability to write it all out in a way that makes it hard to put the book down. None of her mysteries seem formulaic to me, and Adam Dalgliesh (the detective character who is featured in this and many other novels) feels like a real, complex person.
This book features the murder of a nursing student at an old-fashioned English hospital, with a separate boarding school and strict hierarchy for nurses. The atmosphere of this semi-cloistered female community, complete with gossip, malice, and lack of privacy or respect, felt very realistic, and the descriptions of the setting - a Victorian mansion set in a lonely wooded area near the hospital - had just the right level of creepiness. I sure hope that most nursing schools aren't like this one.