Destiny convinces Eternity and Nature that Calisto deserves her own place with them in the heavens.
After an intense war between the gods and mankind, the earth shows the terrible scars of battle. Jupiter and Mercury survey the earth to ensure things are going according to plan. As they continue their investigation, they find Calisto, a nymph, searching for drinkable water. Unable to find any, she shoults at Jupiter in frustration, placing the blame on him. Jupiter is taken aback by her beauty. To impress her, he replenishes the spring and tries making a pass at her. Calisto is an assistant to Jupiter's daughter, Diana, and has vowed to die a virgin just as Diana and her party have done. She quickly rejects Jupiter's advances. Mercury suggests that he should take the form of Diana instead whose charm Calisto will not be able to ignore. Jupiter does as Mercury says, and soon, Calisto is happily receiving Diana's affectionate kisses. The real Diana appears with Lynfea and her nymphs. Endymion is madly in love with Diana, and when she appears, he cannot hide his feelings any longer. As he expresses his love for Diana, Lynfea expresses her anger with him. Diana, too, meets him with cold emotions, but only to hide her true feelings of love for him. Calisto arrives and joins Diana and her party still feeling euphoric from their previous encounter. Diana is confused by Calisto's feelings and actions, so she kicks her out of her entourage. Lynfea wanders off alone and admits that she wants a lover. Satirino, a small satyr, overhears her confession and tells her he'd be happy to serve as her lover- She barely escapes his overealous flirtations. Meanwhile, Sylvano (the god of the woods) and his satyr friends decide to help their fellow satyr, Pane, who has fallen in love with Diana. They are convinced that she is in love with another man, which is why she doesn't accept Pane as her lover. They devise a plan to get rid of her lover.
Endymion peers up into the night sky and observes the moon, which happens to be Diana. After he falls asleep, Diana can't hold in her feelings, so she descends to Endymion's side and kisses him. He wakes up mid-kiss and tells her that their love is just as it was in his dreams. Satirino spies on them in secret. Juno, the wife of Jupiter, descends to earth to check on her husband, feeling he has been unfaithful. She comes across Calisto firts, who immediately confesses that she has been intimate with Diana. Juno suspects that Diana was actually her husband in disguise. Her suspicions are proven right when the impostor Diana arrives with Mercury in search of Calisto. Endymion arrives and rushes to the impostor Diana's side, showering her with flirtations and affections, but his advances get nowhere. After Calisto and Diana leave together, Juno exacts revenge on Calisto. Pane has been spying on them the entire time, unaware that it was Jupiter in disguise as Diana. He believes that Endymion is Diana' lover and quickly calls out to cohorts in order to abduct him. After he is captured, they torture him as they mock true love.
Calisto fondly remembers her passionate encounters with Diana, still not knowing that it was Jupiter in disguise. Juno and two of her henchmen from the underworld confront Calisto. In the heat of the moment, Juno curses Calisto by turning her into a bear. Jupiter confesses that he has fallen in love with Calisto, and admits that his powers are unable to break Juno's curse. However, he will do everything he can to grant her a place among the starts once her life on earth as a bear ends. The real Diana grows more in love with Endymion with every passing day. Pane and the other satyrs realice that they will never be able to win her over, and begrudgingly release Endymion, leaving their love up to fate. Jupiter watches over Calisto saddened by the fact that he cannot turn her back into a nymph. He takes it upon himself to spare her from wandering around the woods alone, so he cuts her life on earth short. As she dies, he escorts her into the heavens and places her as a star in the constellation of Ursa Major, where she will live forever.