Night summons his dark followers to do battle with Dawn. But, for all his show of power he cannot stop her light as it floods over the wooded slopes of the island of Zacinto and he retreats defeated.

Apart from setting the first scene of the opera the prologue is a comment on the ultimate resolution of the plot.

In Dawn’s light Clori comes to meet her lover Lidio. They embrace and exchange vows of everlasting love; even the bark of the trees has been carved to read ‘Lidio lives only for Clori of Delos’ Their vows are suddenly interrupted by a disembodied voice accusing Clori of being unfaithful. Lidio’s jealousy is immediately aroused and the discovery that the voice comes from a man lying asleep with other travelers under the trees does little to abate it. Clori recognizes the man, who had called out to her in his dream, as Egisto, her former lover and, alarmed, she runs off followed by an agitated Lidio.

Egisto and Climene, his travelling companion, awake and we learn that they have both been in servitude to some pirates and having escaped, Egisto has escorted Climene back to her native island where her brother, Ipparco, is the reigning Prince. Climene was formerly pledged to marry Lidio, a native of Zacinto and Egisto, who was born on Delos and is descended from Apollo, is in love with Clori. Egisto despairs of ever seeing her again for they had been captured together and then separated.

Suddenly they see the inscription on the bark of the trees and realize that Egisto’s dream of Clori’s unfaithfulness has come true and Climene’s love for Lidio is betrayed. They vow to be revenged.

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

Ipparco now enters seeking Clori for whom he has an unrequited passion. He knows of her affair with Lidio and is intent on revenge. His cynical old nurse who has followed him, dissuades him from resorting to violence and having promised to speak once more to Clori on his behalf is left to sing a comic solo scene about how to manage love affairs with the minimum of inconvenience.

The scene changes to the Palace of Venus on Olympus.

The Deities of Beauty and Sensuality celebrate their special powers. Their mood of appreciative self-appraisal is only enhanced by the arrival of Cupid in whom they acknowledge a greater strength. Festivities are cut short by the arrival of Venus far from pleased at the way things are going on in Zacinto. She hates Egisto for his kinship with Apollo and is angry that he has escaped from the pirates’ bondage into which she had delivered him and frightened that he may even regain the love of Clori.

Cupid promises to relieve his mother’s anxiety. He will descend into Hell and dip his arrows in the waters of the river Styx, so that he may make Egisto mad and avoid any such reunion. Beauty and Sensuality congratulate Venus, now restored to good humour, on the ingenuity of her son.

Climene, now restored to her brother Ipparco, waits to encounter Lidio. She tries to banish jealousy from her heart but when Lidio enters singing of Clori, it is too much for her and she accuses him violently of treachery in such a way that there could be no hope of reconciliation. Lidio becomes angry and cynical, finally telling Climene that he wants no more of her. She, after an outburst of rage, sadly laments her lost love.

Ipparco, followed by the old nurse discovers Climene in tears and in comforting her, vows a double vengeance on Lidio. The old nurse, in a solo comic scene, points out to the audience the folly of pinning your faith on only one lover. Let everyone follow her example and enjoy the most varied delights of love for as long as they can. Ask any one of her former lovers if she ever disappointed them.

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

The scene changes to the dark woods of Erebus by the river Styx.

Semele, Phaedra, Hero and Dido, four heroines who have died for love, discover that Cupid is in their midst. They chase and catch him determined to make him suffer a fate equal to theirs. As they debate which torture would be most suitable, Apollo, who has heard of Cupid’s plight, appears and tries to appease the Heroines’ wrath. Reluctantly they agree to release him if he will reverse the situation in Zacinto and restore Lidio to Climene and Clori to Egisto. Cupid accepts the conditions but omits to say that he possesses some arrows which have been dipped into the river Styx with which he can send Egisto mad and so also fulfill the promise he has made to his mother. The heroines and Apollo sense that there is some deceit and warn us never to trust completely the little winged God.

Clori and Lidio meet but their love-making is violently interrupted by the arrival of Ipparco and Climene. Ipparco’s guards seize Lidio and tie him to a tree. They lead Clori away leaving him to the mercy of the vengeful Climene. She for all her anger, finds herself powerless to hurt him. Rather she would kill herself. Her spirit of self-sacrifice so moves Lidio that his former love for her is rekindled.

Cupid appears. It seems that the reconciliation of Climene and Lidio was all his doing. Now he must carry out the second part of his bargain and make Clori love Egisto once more. First, though, he can honour his secret vow to Venus by making Egisto mad. He is very frightened by the memory of what those four ladies might have done to him and warns the men in the audience to be extremely careful in their dealings with women.

Egisto is now made mad and in a solo scene shows his crazed, alternating hatred and love for Clori. He has an image of himself as Orpheus seeking his beloved in Hell; of crossing the river Styx in Charon’s boat; and, seeming to see her, follows her as she runs away.

At Ipparco’s palace Clori remains obdurate to the Prince’s protestations which are interrupted by the arrival of the reunited Climene and Lidio. Close upon this comes the old nurse with news of Egisto’s madness and then Egisto himself appears still imagining himself to be Orpheus in search of his Euridice. Out of pity Clori responds to Cupid’s arrow and finds her old love for Egisto revived in her heart. But he is mad.

The seemingly hopeless situation is redeemed by the intervention of Apollo who sends, one by one, the four Seasons to restore Egisto’s sanity and, after a masque-like scene, to transport both Egisto and Clori through the heavens back to Delos and a happy life together.