The Eye of Zoltar - Jasper Fforde

The thrilling final showdown between Jennifer Strange and her most formidable foe.
The Mighty Shandar is back! The most powerful wizard in the world returns to the unUnited Kingdom after failing to solve that pesky Dragon Problem, determined to get rid of the last two remaining dragons once and for all. If he fails, he must return the fee he was paid: eighteen dray-weights of gold, which at current prices is approximately eight trillion moolah (enough to pay for the Fifth Troll War and make a down payment on the sixth). As Shandar's agent, Miss D'argento, affirms: "The Mighty Shandar doesn't do refunds."
It shouldn't be a problem for this Wizardus Maximus, but for one thing: a small House of Enchantment named Kazam stands in his way, led by acting manager Jennifer Strange . . .