Nature and Eternity celebrate those mortals who have climbed the path to immortality. Destiny insists that the name of Callisto (Calisto) be added to the list.
Jove (Giove) and Mercury (Mercurio) are visiting Arcadia. Jove sees the nymph Callisto, a follower of Diana, the virgin goddess of the hunt, and attempts to seduce her. She resists his advances, but finally succumbs when he disguises himself as Diana.
Meanwhile the real Diana, because of her vow of chastity, cannot return the love of the beautiful shepherd boy Endymion (Endimione). Diana is supported by one of her nymphs, the elderly Lymphea (Linfea), who secretly yearns for a husband, but spurns the advances of a young satyr.
On Mount Lycaeus Endymion sings to the moon, the symbol of Diana. As he sleeps, Diana covers him with kisses. He awakes and they sing of their love.
Jove's infidelity is discovered by his wife Juno, while Diana's secret is found out by Pan, the god of the forest, who has long desired her. Endymion is persecuted by Pan and his satyrs.
The Furies turn Callisto into a bear at the command of the outraged Juno. Jove sadly confesses all to Callisto: she must live the rest of her life as a bear, but eventually he will raise her to the stars.
Diana rescues Endymion and they agree that kissing will be the extent of their love-making. Jove, Mercury and Callisto celebrate Callisto's ascension to the heavens.