This is the fifteenth book in Castillo's Kate Burkholder series. Kate is the sheriff in Painter's Mill, Ohio, a town that straddles two worlds: English and Amish. Kate straddles these two communities herself, having been raised Amish. (Why she left the faith is covered in the first book, Sworn in Silence.) That tension and contrast between her past and present, and between the Amish and English in town, is what I love most about this series. There's also a dark edge to these mysteries that make them very compelling reads. This latest is no exception.
A Fatal Illusion by Anna Lee Huber
This is another of my favorite mystery series. It's set in England and Scotland in the 1830s. I always find the historical part interesting, but it's the relationship between the two main characters, Lady Kiera Darby and Sebastian Gage, that I really love. They're a very engaging couple (even though Gage suspected Kiera of murder in the first book, The Anatomist's Wife), and their investigative skills really complement each other. It's best to read this series in order...and it's definitely one worth checking out.