Philippa, the heroine, is not portrayed as a particularly sympathetic character. She's adopted and at the age of 18 applies for her true birth certificate. At the time PD James wrote the novel this was still quite controversial. I remember the change in the law well because I too am adopted. Previous to 1975 in England and Wales it had been assumed that an adoption order made final the split between blood parents and children. The change in the law raised some difficult situations, especially I suspect for the birth mother, who was suddenly confronted with the possibility that her past might in a very real way confront her. Philippa's case is more unfortunate than most when she discovers that her mother is a notorious child murderer and is about to be released from prison. Philippa visits her mother, and arranges for them to move in together, but unknown to her the father of the murdered child is also interested in her mother, and the novel is about to take a very dark turn.
It's pretty well written but I do find a snobbishness in PD James that I never noticed in her novels when I was younger, and this does rather grate. The characters are not particularly well formed - in fact some of the minor characters such as the greengrocer, George, and the blind receptionist, Violet, are realised rather better than many of the major characters. The major characters are all rather unsympathetic, and I did feel that it lacked a sense of what being adopted is really like. I'm not saying that I'm unsympathetic to Philippa's plight, or that I believe that all adoptions were necessarily happy. But I just felt it was a rather exaggerated view of adoption, and certainly there was one scene mentioned briefly between Philippa and her adopted father which for me had the Yeuch factor big-time.
It was just as though PD James had thought long and hard about all the possible pitfalls of being adopted and then picked all the most gratuitously, over-the-top elements she could find. And so for me there was little that was truly believable about it. It's interesting enough as a casual blood curdler, but not something I'd want to re-read.