This book, which was first published in 1977 (and not 1972, as Goodreads suggests) reads like it was written in 1947, if not earlier. It's very much in the tradition of English mysteries that were set in country houses in the years between the two world wars, and there's nothing in the book to suggest the time period in which it is supposed to actually take place. There are a number of young men and women in the book, but they don't sound remotely like the young people who were living in England in the '60s and '70s; rather they sound much more like characters who would ultimately become the parents of those young people. P. D. James was 57 at the time this book appeared, which suggests that she probably didn't have a lot of contact with the young people of that era and didn't begin to understand them.
The protagonist is a plucky female detective named Cordelia Gray, who also sounds like she just stepped out of the 1940s. She inherits the detective agency where she's worked for only a brief period, when her partner commits suicide after learning that he has cancer.
Following the partner's funeral, Cordelia is asked to investigate the suicide of a young college dropout named Mark Callender. Callender's father is a prominent scientist who didn't have much contact with his son, but he tells Cordelia that he needs to know why his son would have hanged himself. Cordelia accepts the case and promptly moves into the primitive country cottage where the boy took his life, apparently to be as close as possible to the investigation.
It will come as no surprise to anyone who's ever read a crime novel, let alone one in this particular sub-genre, that before long our intrepid heroine will begin to suspect that Mark Callender didn't actually kill himself but rather was murdered. Cordelia will question a number of the young man's friends and will go to parties and outings with them as her investigation proceeds. And before long, she will find herself in serious danger.
This is a book that could have been shorter by a good thirty percent. There are endless descriptions of landscapes, houses, clothing and characters that go on and on and on and on unnecessarily. It's also very hard to take the story seriously because it unfolds in ways that often make no sense at all.
That said, this is a pretty good example of a type of book that was once very popular in the mystery genre. Clearly the author had immersed herself in this field before writing the book and she then produced a novel that would have appealed to lots of readers "back in the day." It's hard to imagine, though, that this book would find much of an audience in the modern era. James would later abandon this character after only a few outings and turn to her much more successful and enjoyable (and believable) protagonist, Adam Dalgliesh, who makes a cameo appearance here. Readers curious to sample the work of P.D. James would be much better served by trying one of those novels.