I'm currently storytelling a Delta Green chronicle and, while studying various resources and scenarios, I was extremely intrigued by a scenario called "The Bookstore". That is a great opportunity to give the characters some Cthulhu mythos points and help them get a useful tome or artifact. I would like to extend that scenario and I'm looking for ideas.
In order to extend the question and make it more useful for storytellers:
What tropes do you think fit in an old "Antique Store", "Bookstore" or even "Library"? Do you have any relevant film/comic references (for example, the "Gremlins" movies and "The Occultist" from DC Comics)? Any similar scenarios you've played?