Please, if this is the first Rendell and/or Wexford you've read, don't judge her by it. It isn't typical. Try Shake Hands For Ever, or From Doon with Death. Or A Demon in my View, or A Judgment In Stone. Or most of her earlier books.
This one is a major disappointment in a usually excellent series. The main plot, about a man whom Wexford has suspected of past murder and who becomes a prime suspect for a new murder, is flaccid, meanders all over the place, really has little suspense, and goes out with a whimper. (Even Wexford is disappointed!) The secondary plot, about a Muslim family in Kingsmarkham whose daughter may or may not be subjected to a forced marriage, is offensive, heavy-handed and ludicrous. I have no idea of Ruth Rendell's intent with the Tamima plot. A female detective sergeant and a respected schoolteacher basically harass a family because their daughter isn't going to a sixth form college after taking O levels. It seems Rendell is trying to make a point about misguided attempts to avoid being prejudiced, or about the racism that none of us can fully escape. But it is just not credible that any police officer would be allowed to proceed as Hannah proceeds, on zero evidence. At times Hannah and her teacher cohort are made to look so ridiculous that you think they must surely desist, author's point having been made, but no. Rendell in fact allows a kind of vindication late in the book.
Both plotlines are drawn out to the nth degree, with repetitive scenes of the police questioning people and/or talking amongst themselves. To make matters worse, there is a third plot of a sort, Wexford's reminiscences about his early career. These passages won't have much meaning for people who are new to the series, and for those who are not, they seem superfluous - tacked-on. Having read the books, I already know Wexford. In fact, the way his character has always been revealed through the storyline is one of the strengths of the series. To be given details about his early days on the beat, how he met Dora, and so on, is unnecessary and really not very interesting.
The book isn't very long, but it reads like a 600 pager. Again I suggest reading almost any of the rest of the series. This just isn't a good example.