In this first in a new series, the third graders of the Pet Lovers' Club organize a Halloween party to benefit a local animal shelter; unfortunately, class bully Dirty Donald promises to come. Scared of Donald and sad that his beloved dog Roll has been sent away, Bernie decides to stay home; but once he's allowed to keep an affectionate stray he names Elton, he changes his mind--dyed black and fitted with fake fangs, Elton makes a convincing enough werewolf to scare the daylights out of Donald. Later, Elton coaxes Donald out of his previously concealed fear of dogs, while Donald and Bernie become friends. Roos appends a dog-care checklist for readers to fill out--and advice for werewolf owners, too. Succeeding volumes will doubtless focus on other club members' pets. No surprises here: formulaic but readable and wholesome.