Peachy and Keen Book #3: The Haunted Halls

It's Halloween at Happy Tails School and Peachy and Keen want to uncover what's really making that "Ooooo" noise coming from the locker rooms and write about it for Purrfect9.

But when they sneak into school after hours, they discover something they weren't quite ready for. Could Happy Tails School be home to a spooky ghost or is there some other explanation for all of that spooky singing?