I have been a lifelong reader of Agathe Christie's detective stories; recently I decided to try her "straight" novels. Their main interest lies in the psychology of the protagonists; and it is fascinating to read a detailed psychological profile of certain types that have often been encountered in Christie's detective fiction. They are romances, but in a rather unusual way, as each book (of the four I have read so far) deals with a case of love, not always romantic, but either slightly perverted or inadequate.
The central character of this story is a person (usually female) who has appeared several times in the author's detective stories, almost always in the role of the victim: the complete egoist. She is not consciously selfish or intentionally cruel, but so completely self centered, that all her thoughts, actions and feelings refuse to allow any other point of view than her own. She lives in a world where she is the center of the universe and other people are as two-dimensional and no more real than fictional characters. Usually, she goes though life oblivious of other people's nature and feelings, causing harm to them, because she loves herself too much and them not enough to make the effort of seeing them as they really are. In this book, she suffers an epiphany and comes face to face with her true self as well as the reality of her life; the resolution is somewhat surprising, but when it happens it feels inevitable.
The only reservation I have, in this as in other books by Westmacott, is the religious element. There is a "St.Paul on the way to Damascus"-type revelation that might jar readers' religious feelings, but it can be easily overcome, as it is neither an attempt to convert or offensive in any way.