A Rather Unhelpful Post, But Hey You Got A Potion Good thinking Renwick. There are no more keys to be found, but you do find a green potion in the Kitchens, and there's some magical stuff radiating in the fountain and greenhouse of the Botanical Gardens, but that's previously unexplored territory... let me know if you want to go there.

The Book of Familiar Places, oddly, is completely blank. There are 10 heavy pages in the book.

Brogg, the little golden key will not unlock any other cases. One key, one case.

...

You talk to Meeks some more.

"Keys? Leave those books be. Magical tomes, feed them to me. The royalty preserved them, the other Master of the Archives, those upstairs, corrupted beyond recognition."

"Where did you hear that word? No, forget it, beyond lies the source of madness. It was our error. Do not repeat it. Mirrors are seductive, fool. Learn from our sickness. We possessed it, yet our world still collapsed. Think yourselves better?" He laughs.

"There is no challenge that lies ahead. There is only the annihilation of the self. Gaze upon me. Look at the others. It will..."

...

Brogg, what folio are you talking about? Not the four leaf one with the quatrains and sonnet... that was un-removable. Please remind me.  ¶ 12:29 PM