Diana Wynne Jones 
Archer’s Goon [EPUB ebook] 

Fact: A Goon is a being who melts into the foreground and sticks there…When the Goon turns up demanding "Archer’s two thousand", life turns upside-down. As Howard desperately tries to get to the bottom of this peculiar demand, he discovers that the town is run by seven crazy wizards (not all of whom live in the present!) and someone is trying to take over the world!Exciting, bizarre and truly hilarious!