While cleaning up the library, Twilight finds an old book she's never seen before. It turns out to be an old diary that was clearly owned by a young filly, but only the first page has any writing on it. The rest of the book is blank, but Twilight senses there's something hidden.

She assumes it's some harmless spell or secret ink that foals use to keep their journals secret, but something strange happens the second Twilight uncovers the words on the next page. This should be more than enough to convince her to leave the book alone. It's clearly dangerous, but Twilight becomes hooked on finding out what this diary is hiding, and the truth becomes more horrific than the dangers she finds herself in.