This is Book four in the Fiona Griffiths series. (I highly recommend you read these in order. The plots have some degree of continuity, and they are best enjoyed consecutively.)
This time around, our defective detective heroine joins the dots between a couple of suicides and some burglaries. While the plot stretches credulity a teensy weensy bit, the central character remains as compelling as ever, and the force of her personality easily glosses over any shortcomings there. If you can suspend your disbelief, it does all fit together very well, and is superbly unpacked by the author with great timing and increasing tension as the forces of law and order try to work out what is going on. Inevitably some DIY policing by Fiona Griffiths makes the difference, and her exploits are maniacal, dangerous, and thoroughly entertaining.
Of the four books so far, this was the weakest, but only by a whisker. It is still an excellent piece of crime fiction, with wonderful storytelling to accompany the stunning main character. The backdrop of Wales continues to do its bit in establishing the unique nature of the series, and some of the supporting characters are slowly beginning to get some heft behind them.