The spirit of music invites the audience to listen to the story of Orpheus (Orfeo), whose music could tame wild animals and conquer the underworld.
In the fields of Thrace the marriage of Orpheus and Eurydice (Euridice) is being celebrated. Orpheus sings a song of love and praise. The nymphs and shepherds share in his joy as they accompany him to the temple.
Orpheus sings to the woods, but his mood of celebration is ended by the arrival of Sylvia, who tells him of Eurydice's death from a snake bite. He is overcome with grief, but resolves to bring Eurydice back from Hades.
Orpheus is led by Hope (Speranza) to the gates of Hell, where she leaves him.
At the River Styx he sings to the boatman Charon ("Possente spirto, e formidabil nume" - Powerful spirit, formidable god), who pities him but does not let him cross. After more singing from Orpheus, Charon falls into a deep sleep. Orpheus takes the oars and crosses the river.
In Hades, Proserpine (Proserpina), who has heard Orpheus's music, begs her husband Pluto to allow him to return to earth with Eurydice. Pluto agrees on condition that Orpheus leads her out of the underworld without once looking back. On their journey home, Orpheus begins to doubt that Eurydice is behind him and, hearing a sound, he turns back and Eurydice vanishes before his eyes. Orpheus continues alone, accompanied by the lamentations of the chorus.
In the fields of Thrace, Orpheus pours forth his grief, but is answered only by Echo. He vows to renounce women. His father, Apollo, descends from the skies in order to console him. Together they ascend to the heavens, where Orpheus will once again see Eurydice in the sun and the stars.