No Such Thing As Ghosts — Ursula Vernon

Danny Dragonbreath and his best friend, Wendell, have a carefully constructed trick-or-treating system designed to maximize their Halloween candy haul. But this year, despite Danny's awesome vampire costume, their plan is flopping. First, Danny's dad makes them trick-or-treat with Christiana Vanderpool, an annoying know-it-all (and girl) who doesn't even believe that dragons exist. And then the school bully dares them to go into a spooky old haunted house. Naturally, the house is inhabited by a creepy clown and a candy-crazed ghost of yore. It's going to take more than fire-breathing to get them out of this mess - they might even have to (horror of horrors!) perform a sacrificial candy offering.