Julia Spencer-Fleming is one of the very best at portraying the nuanced personal relationships of her characters. The marvel is that she does this and creates a fantastic mystery, too. Periodic chapters from little Mikayla's point of view definitely keep the sense of urgency at the boil as do isolated locations and horrendous winter weather.
Some of the behavior of Russ and Clare (particularly Russ) almost had me talking to myself-- not that I'm totally wrapped up in these characters or anything-- but the mystery is just as good as the author's characterizations. I enjoyed myself trying to deduce the identities of everyone involved with Mikayla's kidnapping, and watching all the various plot threads coming together was a delight. For any of you who may be as interested in the relationship between Hadley and Kevin as I am, there's plenty of that in Through the Evil Days.
For those of you who love marvelous characterization every bit as much as you enjoy trying to solve mysteries, I can't recommend Julia Spencer-Fleming's series highly enough. There's only one catch: since the lives of the characters play such a large part in the books, if you're new to the series you should really begin at the beginning with In the Bleak Midwinter. Oh, the treat you have in store!