Night summons his followers to battle with Dawn. But, for all his power, he cannot stop her light as it floods over the island of Zacinto. He retreats.

Clori comes to meet her lover Lidio, and they exchange vows of love. The bark of the trees has been carved to read “Lidio lives only for Clori.” Their vows are interrupted by a voice accusing Clori of being unfaithful. Lidio’s jealousy is aroused, and he discovers that the voice comes from a man lying asleep under the trees. Clori recognizes the man as Egisto, her former lover, and she runs away.

Egisto and Climene, his travelling companion, awake. They have been in servitude to pirates, and, having escaped, Egisto has escorted Climene back to her native island, where her brother Ipparco is prince. Climene was once pledged to marry Lidio, and Egisto is still in love with Clori. Suddenly they see the inscription on the trees and realize that Egisto’s dream of Clori’s unfaithfulness has come true and that Climene’s love for Lidio is betrayed. They vow to be revenged.

Clori returns alone, her conscience troubled by seeing Egisto. But her new love for Lidio has the greater power, and she cannot deny it.

Ipparco, accompanied by his old nurse, enters seeking Clori, for whom he has an unrequited passion. He knows of her affair with Lidio and is intent on revenge.

The scene changes to the palace of Venus on Olympus. The deities of Beauty and Sensuality celebrate their powers. But the festivities are cut short by the arrival of Venus. She hates Egisto and is angry that he has escaped from the pirates, and frightened that he may regain Clori’s love.

Cupid, her son, promises to descend into Hell and dip his arrows into the river Styx, so that he may make Egisto mad. Beauty and Sensuality congratulate Venus on Cupid’s ingenuity.

Climene, returned to her brother Ipparco, waits to meet Lidio. She tries to banish her jealousy, but when Lidio enters singing of Clori it is too much for her, and she violently accuses him of treachery. Lidio tells Climene that he wants no more of her; after an outburst of rage, she laments her lost love.

Ipparco discovers his sister Climene in tears and vows a double revenge on Lidio.

Egisto wanders alone, reflecting on Clori’s unfaithfulness. They meet, and she pretends not to know who he is. Finally, she runs away, leaving Egisto to his sorrow and loneliness.

The scene changes to the woods of Erebus by the river Styx. Semele, Phaedra, Hero, and Dido – heroines who have died for love – discover Cupid in their midst and catch him, determined to make him suffer a fate equal to theirs. Apollo appears and intercedes on Cupid’s behalf. The heroines agree to release Cupid if he will reverse the jumbled situation on Zacinto and restore Lidio to Climene and Clori to Egisto. Cupid accepts these conditions, but omits to say that he has the poisonous arrows.

Clori and Lidio are interrupted by Ipparco and Climene. Ipparco’s guard ties Lidio to a tree and leads Clori away. Climene now has the chance for her revenge, but she finds herself unable to hurt Lidio, and her spirit so moves Lidio that his love for her is rekindled.

Cupid appears; now he must carry out the second part of his bargain and make Clori love Egisto again. First, though, he must honor his vow to Venus, and he makes Egisto mad.

In Ipparco’s palace, Clori and Ipparco are interrupted by the arrival of the reunited Climene and Lidio. Close behind come the nurse, with news of Egisto’s madness. Then Egisto himself appears. Out of pity for Egisto, Clori responds to Cupid’ arrow, and her love for Egisto revives. But he is still mad.

This seemingly hopeless situation is resolved by the intervention of Apollo, who sends one by one the four Seasons to restore Egisto’ sanity and to transport him and Clori through the heavens to the island of Delos and a happy life together.