In 1867, a strict 94-year-old librarian in Port Royal, outside London, died when a stray cannonball hit her library and set it on fire. Everyone assumed Miss Applebottom and her thousands of books were gone for good.

Then people started dying.

Days after the fire, several residents were found strangled in their beds, with no signs of a struggle. Police discovered a handwritten list with seven names, each matched to a borrowed book and an overdue date. Every name was crossed out.

Investigators returned to the ruins of the library and found a hidden door behind a scorched bookcase. It led to a basement no one knew existed. What they saw there was never fully written down, but the last surviving officer later revealed one detail:

“She wasn’t down there,” he said.

“She was behind us.”