Library horror: A vignette

I was having a conversation with a friend to generate some ideas for a game they are running in which one of the characters (an archivist) is experiencing a hallucination, and one of the kernels of dream-logic conversation ended up with me writing a bit of librarian horror, which I am sharing here now that the players have actually played through the relevant scenes and so this won't be a spoiler for them.

( Horror behind cut tags. No jump-scares involved. )