With this title, Walpole established the Gothic as a literary form in England. It was first published as a scholarly translation from an ancient Italian text, a supernatural tale of a fatal prophecy set in the time of the crusades and one which inspired terror in its early readers.

On the day of his wedding, Conrad, heir to the house of Otranto, is killed in mysterious circumstances. His calculating father Manfred fears that his dynasty will now come to an end and determines to marry his son's bride himself - despite the fact he is already married. But a series of terrifying supernatural omens soon threaten this unlawful union, as the curse placed on Manfred's ancestor, who usurped the lawful Prince of Otranto, begins to unfold. First published pseudonymously in 1764, purporting to be an ancient Italian text from the time of the crusades, The Castle of Otranto is a founding work of Gothic fiction. With its compelling blend of sinister portents, tempestuous passions and ghostly visitations, it spawned an entire literary tradition and influenced such writers as Ann Radcliffe and Bram Stoker.