Volume: 11
Release date: September 1993  

The Haunted Mask may have been the eleventh book in the series, but it was the first one that you could find literally everywhere you looked. (Seriously, these things were sold everywhere from supermarkets to car washes.) The story focused on timid 11-year-old Carly Beth, who winds up with an evil Halloween mask she can't remove. The book is insanely thrilling from start to finish, with a twist ending that was just the right amount of horrific ("How do I look in your mask?"). Anyone who's read it will tell you, the thought of it still gives them shivers.