The wizard Zoroastro sees signs that the warrior knight Orlando, madly in love with Angelica, Queen of Cathay, will return to his mission as a knight of valor and recover from his worldly passion. Orlando is torn between love and duty and Zoroastro urges him to forget Venus, goddess of love, and follow Mars, god of war, as he used to. Orlando eventually decides that he can and should combine his knightly deeds with his love of the queen.
The shepherdess Dorinda senses that she might be falling in love. As Orlando rushes through with the princess Isabella whom he has just rescued, Dorinda senses that Orlando too might be in love. Dorinda hides in her hut the queen Angelica who has found the wounded Moorish warrior Medoro and saved him from death. Angelica has fallen in love with Medoro, yet Dorinda has fallen in love with him too. Even though Medoro tries to comfort Dorinda with lies about his relationship with Angelica, she know he does not tell the truth yet is still is enchanted by him.
Zoroastro warns Angelica that once Orlando discovers that she loves Medoro he can be totally unpredictable. As Orlando arrives Angelica confronts him and accuses him for loving Isabella, but Orlando responds that he could love only Angelica and would do anything she asks for to prove that. Angelica advises Medoro that the two should leave to her far away kingdom and thus escape Orlando’s fury and as they leave, Dorinda is left alone, heartbroken.
Dorinda is in total despair over the loss of Medoro and Orlando confronts her demanding to know why she has been spreading rumors about his love to Isabella. Dorinda replies that she was talking only about Medoro and Angelica’s love. Orlando, realizing that Angelica has betrayed him, vows to kill her, kill himself and eventually pursue her also in Hell.
Zoroastro promises to protect Medoro and Angelica from Orlando. Angelica still remembers that Orlando has saved her life once and feels guilty of betraying him, yet she believes he will understand her as he himself is after all also in love. Orlando rushes trying to kill Angelica who is saved only through Zoroastro’s magic. Orlando begins to lose his mind, seeing visions of Hades and is eventually carried away by Zoroastro.
In all the commotion Medoro has been separated from Angelica and has returned to Dorinda’s hut, telling her he would have liked to love her but his heart is Angelica’s. Orlando arrives, declaring his love to Dorinda, addressing her as Venus. Zoroastro appears and transforms Dorinda’s hut into a dark cave where he will try to restore Orlando to sanity. Angelica arrives and Dorinda tells her that Orlando in his madness burned her hut and killed Medoro and as Orlando himself appears, Angelica asks him to kill her as well. Orlando, imagining that he has rescued the world from all monsters, brings Angelica into the cave. Zoroastro manages to restore Orlando into reason, yet as he returns to his senses, he believes he has killed both Medoro and
Angelica and seeks only death for himself. However, Zoroastro has of course saved both Medoro and Angelica and as Orlando sees them alive he wishes them a happy life and everybody celebrates in Dorinda’s restored hut.