Isis was the great Moon Goddess of the Egyptians. She is the protectress of Thyrsa, a beautiful singer, for whom she chooses Prince Dilo as husband, sending him a message to that effect. The prince seeks out Thyrsa, and charmed with her grace and beauty, is more than willing to marry her and discard Sara, his former favorite. Sara, however, jealous of her rival, informs Dilo that Thyrsa has other lovers, and the Prince, giving vent to his scorn and repugnance for the singer, returns to his palace. Thyrsa is humiliated, the more so that she loves Dilo deeply. Heartsick, she carries her grief to the Moon Goddess, who, taking pity on her, declares that Dilo shall be punished. Taking on the form of flesh and blood, she descends from her seat in the temple, and appearing to Dilo in his sleep, creates in his heart a love for herself. Dilo, springing up out of his sleep, follows her blindly until she reaches the temple, when, after slowly mounting the steps to her seat, she changes back into lifeless stone.