The Robe of Skulls

The Robe of Skulls is the first book in the Tales from the Five Kingdoms series by Vivian French.

Summary
All is not well in the crumbling castle high above the mountain village of Fracture. The sorceress Lady Lamorna has her heart set on a new robe. A very expensive new robe. To get the cash she will stop at nothing, including kidnapping, blackmail and more than a little black magic.