Twilight doesn't believe in ghosts, but everyone else seems to. So just to prove it to them, she decides to stay in a haunted house for a while. She writes down everything that happens, but she's sure nothing will happen. Ghosts aren't real. Right?
After a while, she starts to think a little differently.
Cover art credit to SolarFlare-Solis. http://solarflare-solis.deviantart.com/art/Twilight-Sparkle-Scared-318392950