I got my weekly email newsletter from my friendly local bookseller which featured the following blurb:

The 5th Horseman
by James Patterson
On Sale Monday, February 13th
Little Brown, $27.95
Ten years after the smash hit Wicked, the author returns to the land of Oz to follow the story of Liir, the adolescent boy left hiding in the shadows of the castle when Dorothy killed the Witch

WOW! That's the same storyline of the book Son of a Witch by Maguire! Time to start ignoring the Frey controversy--this is a big deal! But somehow this doesn't really fit in with this series.