Any Frightening Mystery Stories For Someone With A Low Attention Span?

The only times I've been scared during movies is while watching them late at night. Session 9 freaked me out because of the abandoned setting, the creepy audio tapes and the fucked up reveal at the end. The Blackcoat's Daughter got me because of the impending doom, the sudden, unexpected violence and one character's overall presence.

I have ADHD, so it takes me awhile to finish books, but I want to introduce myself more to horror literature. I find it thrilling figure out character motivations and how each person's past + identity ties into a singular mystery that effects everyone within the storyline. The show Slasher: Guilty Party is a more simplified version of the format I enjoy, although the gore tended to overwhelm the story at parts. I love Agatha Christie whodunnits; The Seven Dials Mystery was a favorite when I was younger.I have gotten around to a couple Stephen King novels the past few years (The Shining and The Outsider); both of which I enjoyed. Let me know if you guys have any ideas