Christopher Pike 
Pan’s Realm [EPUB ebook] 

Are there fairies and gnomes? Leprechauns and elves? Most people, including Adam, would have said no. But one day a whole herd of magical creatures invades Spooksville. At first they play childish pranks, and Adam and his friends are happy to welcome them. But quickly the pranks turn cruel, and Adam, Sally, Watch, and Cindy are soon fighting for their lives. Where did these little people come from? How can Adam and his pals make them go away?