An old Diary

The interior of the box is lined with soft padding to perfectly fit a single small book. It's simple, featuring a smooth, unmarked leather cover shiny in places from the wear of countless touches. It has the look of a diary. Bri carefully lifts it from the box to examine it further. The pages aren't brittle or yellow, like some old books she'd seen, but as she takes an obligatory sniff, she is rewarded with the pleasant aroma of very old books. Could this be Grandmas diary?

Feeling only slightly self-conscious, she opens the cover to search for clues as to the book's origin. The first page is blank except for a messily scrawled note in pencil near the bottom. Barely legible, in shaky, oddly-formed letters that remind Bri of what it might look like if someone were to write with their weak hand, or any other strange grip.

It's all real.

That's strange. Now more curious than before, she turns the page. Now the letters are neat and deliberate, written in dull black ink with a clear hand covering the entire page. It begins:

This will be my last journal; the others no longer matter. I've finally solved it and will record all of it right here. My life's work, the product of so many years of isolation and study. Magic is not only possible, it's predictable. Deterministic. So easy to miss, but it's all right there.
I digress.
I write this journal for a selfish purpose, to give myself the key to everything I've always wanted. Lord knows I've sacrificed enough for it.

As Bri reads on, her eyes widen in surprise and a small grin parts her lips. This is wild. Why would anyone write this, let alone keep it in a locked chest. She flips through the small book to confirm that it's over half full of writing, including some drawings and diagrams. The author of the journal is clearly obsessed with a very specific idea, and dreamed up an entire book of spells and an impressive introduction to what appears at a glace to be a comprehensive magic system.