Wolfsbane — Patricia Briggs

For the last ten years, shapeshifting mercenary Aralorn has led a dangerous existence -- a far cry from her noble upbringing. Now she must return home under the most unfortunate circumstances. Her father, the Lyon of Lambshold, has passed away. But when Aralorn and her companion Wolf arrive, the combination of their magic uncovers something wonderful yet alarming -- her father is not actually dead, but only appears so. Yet a dark mist is also very much alive within him...

The Lyon of Lambshold has been ensorcelled by the ae'Magi, who's using him as a conduit to finally destroy Aralorn and Wolf. With her father as the pawn, can Aralorn overcome this mysterious sorcery? Or will she finally fall to the blackest of magic, losing not only her one true companion but also her life...?

Wolfsbane is a tightly-coupled sequel to Masques.