Once upon a time, in a far off kingdom, lived an accursed girl, doomed to be "a wretched creature that dwells only in darkness," as declared by a bodiless head who cursed her family line. Things didn't quite work out that way. The protagonist, the titular witch, is instead cursed with eternal youth and beauty, which is a bit of a disadvantage in her line of work, as witches are generally expected to be ugly old hags.
After the murder of her mentor, the protagonist, along with her familiar, a duck named Newt, go on an quest to discover and avenge themselves on the perpetrator. Along the way, they add to their party a Troll, a White Knight, and an animate broom.
This book, described as a tale of "magic, true love, and cannibalism," lives up to that, being a satirical look at fairytale clichés, and how hard it is to find true happiness and love when living as a cursed creature with an appetite for human flesh.