The Eye of Zoltar: Last Dragonslayer Book 3 by Jasper Fforde
The Mighty Shandar, the most powerful wizard the world has ever seen, returns to the Ununited Kingdoms. Clearly, he didn't solve the Dragon Problem, and must return his fee: eighteen dray-weights of gold.
But the Mighty Shandar doesn't do refunds, and vows to eliminate the dragons - unless sixteen-year-old Jennifer Strange and her sidekicks from the Kazam house of enchantment can bring him the legendary jewel, The Eye of Zoltar.
The only thing that stands in their way is a perilous journey with a 50% Fatality Index - through the Cambrian Empire to the Leviathan Graveyard, at the top of the deadly Cadair Idris mountain. And it's a quest that sees Jennifer fighting not just for her life, but for everything she knows and loves . . .