Perseus is brought before King Cepheus and Queen Cassiopeia, who are celebrating their campaign against the gods. Queen Cassiopeia brashly compares her daughter Andromeda to the gods and boasts that she is more beautiful than Aphrodite. The revelry is cut short by the arrival of Hades, who has been given leave by Zeus to punish the mortals for their defiance. Hades threatens to unleash his monster the Kraken against Argos, unless Andromeda is offered as a sacrifice. Before leaving, he reveals that Perseus is a demigod and the son of Zeus.
Perseus meets Io, who confirms his origin. Io also reveals that she has watched over Perseus his entire life. She has always protected him for he is the only one who can defeat the gods.