Boo! is the story of a young girl's trip to the dentist on Halloween. She has a very active imagination that is fueled by each step of the visit from pulling up in front of the dental office to meeting the receptionist to meeting the hygienist, etc. The illustrations go back and forth from what she imagines to what is real. The receptionist is a goblin until she isn't. The hygienist is a witch until we meet her. The dentist is a vampire--but no. The empty couch in the waiting room is a time machine operated by gargoyles. The chair in the corner is obviously a Venus flytrap chair. However, it is true that looks can be deceiving. Find out for yourself if Katy and her imagination are on to something.