The Dunwich Horror by H.P. Lovecraft

In the meantime a quieter yet even more spiritually poignant phase of the horror had been blackly unwinding itself behind the closed door of a shelf-lined room in Arkham. The curious manuscript record or diary of Wilbur Whateley, delivered to Miskatonic University for translation, had caused much worry and bafflement among the experts in languages both ancient and modern; its very alphabet, notwithstanding a general resemblance to the heavily shaded Arabic used in Mesopotamia, being absolutely unknown to any available authority. The final conclusion of the linguists was that the text represented an artificial alphabet, giving the effect of a cipher; though none of the usual methods of cryptographic solution seemed to furnish any clue, even when applied on the basis of every tongue the writer might conceivably have used.

The ancient books taken from Whateley's quarters, while absorbingly interesting and in several cases promising to open up new and terrible lines of research among philosophers and men of science, were of no assistance whatever in this matter. One of them, a heavy tome with an iron clasp, was in another unknown alphabet -- this one of a very different cast, and resembling Sanskrit more than anything else. The old ledger was at length given wholly into the charge of Dr. Armitage, both because of his peculiar interest in the Whateley matter, and because of his wide linguistic learning and skill in the mystical formule of antiquity and the Middle Ages.