Upon his return from battle in the previous film, the great warrior Hercules learns that his lover, Daianara, has lost her senses. Acording of the oracle Medea, Dianara's only hope is the Stone of Forgetfulness which lies deep in the realm of Hades. Hercules, with two companions, Theseus and Telemachus, embarks on a dangerous quest for the stone, while he is unaware that Dianara's guardian, King Lico, is the one responsible for her condition and plots to have the girl for himself as his bride upon her revival.

As Garibaldi's troops begin the unification of Italy in the 1860s, an aristocratic Sicilian family grudgingly adapts to the sweeping social changes undermining their way of life. Proud but pragmatic Prince Don Fabrizio Salina allows his war hero nephew, Tancredi, to marry Angelica, the beautiful daughter of gauche, bourgeois Don Calogero, in order to maintain the family's accustomed level of comfort and political clout.

In the 19th century, a sadistic nobleman terrorizes the members of his family. He is found dead, but his ghost soon returns to haunt the residents of his castle.