I have always liked Margaret Yorke's books, even though I haven't liked them all equally. When she's good, she's great; when she's not so good, she's about average. I would put this one in her "second tier," in that it's not one of her best, but it's also not one of her worst.
A CASE TO ANSWER is more "novel" than it is mystery, suspense, or thriller, and that's primarily because the plot is not intense. A young troubled woman comes to stay with her step-grandmother and meets up with a local teenager who's been on the wrong side of the law but is trying to clean up his act. As always, Yorke sets up the family dynamic well (yes, it seems that English families are just as dysfunctional as families everywhere else) and also chooses one or two characters to really explore. In this case, one of them is Charlotte Frost, who remarried after 20 years as a widow, only to find her husband dying after two years of marriage. Despite Charlotte's happy marriage and general aggreeableness, her late husband's children treat her as a burden and see her as standing in the way of their full inheritance.
There's a plot twist halfway through that won't surprise Yorke readers, as we know her tricks by now!
In a lot of ways, this book reminded me of P.D. James' INNOCENT BLOOD. It's an intense and absorbing read, but mostly "internal," without a lot of external action to drive the plot. So if you are looking for a crime novel set in the English countryside, with strong characters and strong, no-nonsense writing, I can recommend it. If you want a book with a stronger plot and more twists and turns, I'd try FALSE PRETENSES instead.
A word of warning: If you are new to Yorke, be sure to read up on some of the reviews on Amazon and other places to make sure you're getting one of her good ones. If you start with a less-good one (such as SPEAK FOR THE DEAD, which really is not good at all), you probably won't read more Yorke, and that would be a shame.