Nancy, Bess, and George are gearing up for a weekend of River Heights Halloween activities, including the annual Howl-A-Ween Pet Parade! All the kids get to dress up their pets and march with them up Main Street. Nancy's dog, Chocolate Chip, is even picked to lead the parade atop a festive hay wagon float!

But right before show time, Chip starts whining, running in circles, and burrowing into the hay! When Nancy can't calm her down, the parade officials remove her as the leader!

Nancy, Bess, and George wonder if something--or someone--made Chip act that way. Nancy pulls out her clue book; the Clue Crew is on the case! Who's behind Chip's strange doggy behavior? Is it Deidre Shannon, who was mad that Chip was chosen over her princess puppy Pom-Pom to lead the parade? Felipe the Pet Trainer, who wanted a dog he was training to lead the parade? Or is it--yikes!--the ghost of Murray the Monster Mutt? Will the Clue Crew crack this case before all the River Heights pets go batty?