This is by far and away one of my favorite book series of all time. It only seems to get better with each book. The mysteries are always so well done, but the series' true strength lies with its characters. Sebastian and Hero are at (or at least near) the top of my all time favorite fictional couples list. Separately, both are complete and interesting characters that you really care about, neither is dependent on the other to prop them up. This makes reading about their ever-deepening relationship all the more satisfying...at least for me.
Aside from them, the other recurring characters are also fully three-dimensional, whether I like them or not.
The thing that was really interesting about this book is that Hero and Sebastian (and their infant son) are taken out of their normal London setting and are thus are the only two series regulars to appear in this book. It was a nice change of pace in such a long running series.
While Hero and Sebastian are visiting the village of Ayleswick-on-Teme, a young woman is found dead and Sebastian is asked to help investigate. During the course of the investigation, Sebastian discovers that the unfortunate young woman has set out on a journey of discovery that mirrors his own and is thus is even more determined to make the guilty party pay. The list of suspects is long, and there are secrets hidden behind almost every door.
With this book being set in a village, it would also be perfect for Terror in a Small Town. Other squares it would fit would be Murder Most Foul, Slasher Stories, and Terrifying Women.