Prologue

In the depths of the cosmos Nature and Destiny meet to guide the valiant souls into the heavens. The god Mercurio tells them that, by Giove's command, Calisto should be admitted into the firmament as an eternal constellation of stars

Act I

After having burnt the Earth for its evils, Giove, accompanied by trusted Mercurio, surveys the planet to restore it. Suddenly Giove is captivated by the appearance of the nymph Calisto, who desperately seeks water in the charred forest. Mercurio warns Giove that she is a member of Diana's band of warrior-nymphs, sworn to spurn love and remain virgins; but Giove ignores Mercurio, appearing to Calisto and making a spring erupt before her. At first full of joy and wonder, she then turns defiant and flees upon learning that he is the God of gods, and that he seeks to woo her. Left alone Mercurio suggests a plot to disguise Giove as Diana and in that way seduce Calisto. When she returns to find what appears to be her goddess, she is indeed pliable to love's advances; and as the giddy lovers run off, Mercurio muses on the value of deceit.

Endimione, a star-gazing mortal, has fallen in love with the moon, which is personified in the form of the huntress-goddess Diana, who secretly feels the same. Meeting each other in the newly restored woods, they hint at their feelings, but Diana's chief warrior-nymph Linfea spurns the suitor’s advances, and Diana too must pretend to castigate Endimione. At the same time Calisto appears, fresh from the joys of physical love. Mistaking the real Diana for the fake one, she seeks to rekindle their flame. In this way she reveals how she broke her vow of chastity, and Diana expels her unkindly from the forest. Left alone, Linfea confides that she too wonders at the nature of love and is torn between her virgin pride and her insatiable libido. Just then the half-goat boy Satirino appears and takes a fancy to the warrior-nymph who, repulsed by his goat-like appearance, rejects him. He swears revenge.

Pane, god of the goats and the woods, wanders the forest looking for relief for his broken heart. He himself is also in love with Diana but she, claiming modesty, rejects his advances. His cries and howls echo through the forest until Satirino and his sidekick Silvano put the weary and depressed god to rest as night falls over the forest.

Act II

In the dark of night Endimione has climbed a mountain peak to be near the moon he loves so much. Just before Diana rises in the sky in her silver moonlight glory, he falls asleep. She looks down upon him as he dreams of holding her in his arms, and she cannot pull herself away. Upon awakening Endimione learns that she loves him as well, but before they can celebrate their mutual attraction, Diana leaves and he is left only with the beautiful memory of their chaste night together. Unfortunately, Satirino was also on the mountaintop spying on them, and swears to tell Pane of Diana's unchaste love and of this mortal paramour.

Giunone, the wife of Giove has heard rumors that her husband is using deceit to seduce a young nymph. No sooner has she come to find him that she meets Calisto herself, who wanders lost and dejected. Giunone immediately understands the situation; but though she tries to tell Calisto, when Giove appears dressed once more as Diana, the young nymph falls for his ruse again. Giunone feigns ignorance and approaches Giove/Diana, questioning her as to what she is doing in the woods and why she is accompanied by Mercurio, the god of lies. It’s clear through her thinly veiled threats and innuendos that she is onto Giove, and when she leaves he is left both infuriated and terrified. Unfortunately for him, Endimione also mistakes him for the real Diana, and seeks finally to embrace his beloved. At the same time Pane and Silvano arrive, led by Satirino. Mercurio and Giove make a quick escape, giving over Endimione to the hands of the angry and violent Pane.

Just before running after them, Satirino spies Linfea. Linfea sings decidedly of her desire to find a husband. This time the young Satirino makes no proposals but tries to take her by force.

Act III

In the darkest and most terrifying part of the forest Calisto waits with great anxiety for her goddess to appear. Giunone, however, finds her first, and riddled with jealousy transforms the innocent nymph into a bear-like beast, before releasing her twin Furies to torment her. Giove and Mercurio chase after them, repentant of their rash and thoughtless behaviour, finally destroying the Furies and promising Calisto that at the end of her life she will rise up to be a constellation in the heavens.

Pane, Silvano and Satirino torment Endimione, deciding not to kill him but to make him live forever tied to a tree. The real Diana appears, chasing off the rude goat-gods, and finally admitting openly her love for Endimione. They decide to consummate their love with a single kiss before living forevermore in chaste admiration of each other from afar.

At the end of time the celestial choir gathers, and welcomes Calisto into the firmament, made eternal as stars in the night sky.