On the day of his wedding Conrad, heir to the house of Otranto, is killed in mysterious circumstances. Fearing the end of his dynasty, his father, Manfred, determines to marry Conrad's betrothed Isabella, until a series of supernatural events stands in his way. A giant helmet falls from the moon, a portrait sighs, a statue bleeds and spirits warn of impending tragedy, as the curse on Manfred's house inexorably works itself out.