Hilda: Magic on the Rocks — Paul Kater

Book 10 of the series around Hilda the Wicked Witch. Hilda and William receive a visitor with a peculiar message. Things in the land of the magicals are going very wrong as wizards and witches start to have problems. One thing leads to another, and through all of this the magical heroes are facing snow and ice, which doesn't make things much easier. Fortunately they don't have to face these challenges alone.