Number 13 by M. R. James

A scholarly visitor staying in an old, out-of-the-way lodging becomes obsessed with a mysterious, out-of-place room whose number seems to have no right to exist; as he and his colleagues probe its history they uncover traces of a long-buried presence and a set of uncanny, medieval clues, and a late-night confrontation with a spectral figure brings the building’s hidden, violent past terrifyingly to light.

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