A most excellent book by Laura Underwood. I've read a short story or two by her and she's a wonderful author, very good with settings, but without going on and on about it. The Hounds of Ardagh is a good read for YA or adults. Its unique in that the main character, Ginny, is saddled with a ghost to help her on her adventures rather than a live counterpart. The ghost is her old teacher Manus and unfortunately he died before he taught her everything a mage needed to know. Ginny also has her teacher's old terrier to hinder her in her adventures (and the author must be familar with the breed of constantly barking dog).
Mainly, Ginny finds herself investigating what has happened to entire village of people--all of whom have disappeared. She is chased by demons and a bloodmage who is on the hunt for a good sacrifice or two. It's a roaring good adventure in a medieval magical setting.