Archer's Goon by Diana Wynne Jones

The trouble started when Howard Sykes came home from school and found the "goon" sitting in the kitchen. He said he'd been sent by Archer. But who was Archer? It had to do with the 2,000 words that Howard's author father had failed to deliver.

It soon became clear not only that Archer wanted those words, but that his wizard siblings, Hathaway, Dillian, Shine, Torquil, Erskine, and Venturus, would also go to any lengths to get them.

Although each wizard ruled a section of the town, he or she was a prisoner in it. Each suspected that one of them held the secret behind the words, and that secret was the key to their freedom. Which one of them was it? The Sykes family become pawns in the wizards' fight to win their freedom, wrest control from one another, and fan out to rule the world.

Diana Wynne Jones skillfully guides the reader through a riveting, twisty plot, with satisfying surprises at every amazing turn. An exciting science fiction adventure where, happily, nothing is what it first seems to be.