Showing Not On My Patch by Diane Duane

In this tale of a unique Halloween in the Young Wizards universe, tag along with Nita Callahan, Kit Rodriguez, Ronan Nolan, and Dairine Callahan as they do a little overage Trick or Treating in their own neighborhood, and find themselves going up against a dangerous old adversary in company with a peculiar new ally... This story, along with "How Lovely Are Thy Branches" and "Young Wizards: Lifeboats," forms a transitional trilogy of canonical works bridging Young Wizards book 9, "A Wizard of Mars," and the upcoming book 10, "Games Wizards Play." The compendium volume, "Interim Errantry", is also available on Amazon.com.