The Mighty Shandar returns to the unUnited Kingdom because he clearly didn't solve the Dragon Problem, and is being asked for his fee to be returned: Eighteen dray-weights of gold, which at current prices is approximately eight trillion moolah, enough to pay for the planned Fifth Troll War and a down payment on the sixth.
The most powerful wizard the world has ever seen is back to get rid of the last two remaining dragons once and for all.
As Shandar's agent Miss D'argento tells us: "The Mighty Shandar doesn't do refunds."
Simple enough - after all, he is the most powerful wizard the world has ever seen. But for one thing: a small House of Enchantment named Kazam stands in his way, led by acting manager Jennifer Strange...