Magic exists, and you need to destroy books to make it happen. More than that, the books need to be powerfully-written and have something to do with the effect you want. Fiction works better than nonfiction. Worst of all are books of nonfiction that purport to be divine or supernatural in any way. Goodnight Moon is good for a sleep spell. Agatha Christie books are good for poisonings.
Librarians dedicated to keeping sorcerous books out of the wrong hands hide the books in plain sight, in a large university library. The books sit openly on the stacks, but they are not cataloged. Their spine labels indicate call numbers that do not actually exist in the Library of Congress cataloging system. Our protagonist gets suspicious because he's a cataloger, and he passes by a book that Doesn't Seem Right. Alas for him, his activities have been noted. A hidden camera watches every forbidden book, though at a distance, since mechanical devices tend to fail around the strange tomes. For that reason there's also the Sleepy Student brigade, slumped at strategic positions with Secret Service style earphones and cell phones. Their job is to identify, follow, and perhaps delay the perusers of the forbidden texts until a senior librarian can arrive. (Other permutations: Books with UV markings and librarians with special dark glasses for reading them; dummy books; books composed of tomes sliced up and spliced together, making it difficult for one peruser to check out a whole text without serious effort.)
A device that has stored a group of photons, "frozen" them so they cannot propagate. The photons encode the locations and passwords to critical computers on the global net, computers which have already been infected by a virus, but lack only the proper trigger to become "zombies," at the command of the device's master. The device has the appearance of an ancient grimoire, bound in dubious leather.
A Thousand and One For All
A librarian in a fantasy world is charged with weeding books. One ancient book refuses to go gently and promises to tell the librarian a new story each day the librarian keeps it in the library...