Teseo

Act 1

Teseo is engaged in battle against Athens' foes as the opera begins. Princess Agilea, the ward of King Egeo, is concerned for Teseo's safety, as she confides to her companion the young maiden Clizia, for Agilea has fallen hopelessly in love with Teseo. Clizia has a boyfriend, Arcane, whom she promises to love always, but when she asks him to find out what he can about Teseo's safety, he becomes jealous.

The Athenians have been victorious in battle, and King Egeo declares that his announced marriage to Medea, a sorceress, is now no longer suitable for such a mighty sovereign as himself and he will take Princess Agilea as his bride. Agilea bewails her cruel fate, having no wish to be a Queen, but to be allowed to marry the man she loves, Teseo.

Medea is furious at the humiliation caused to her by the King's rejection; she is somewhat mollified when the King comes to her and suggests she marry the hero Teseo instead of him as she is in fact in love with Teseo already.

Act 3

Arcane, who is jealous of Teseo because of his misinterpretation of his sweetheart Clizia's concern for him, warns the King not to trust Teseo who, Arcane suggests, will want to throw Egeo off the throne and take his place now that he has become such a military hero.

Medea meanwhile sows seeds of distrust in Teseo's mind – the King is jealous of him, Medea says, and only she knows how to treat the King to allay this bad feeling. Teseo tells Medea he trusts her to put the situation right. Medea, full of hatred, vows revenge for the insults she has suffered.

Arcane has decided to put his jealousy behind him and seek marriage to Clizia.

The King, learning that Agilea is in love not with him but with Teseo, does not wish to force her to marry him and has given his consent for Agilea and Teseo to be united. The lovers are overjoyed at this news but Medea, insulted and rejected once more, bursts into the room where Agilea and Teseo are celebrating their reunion and, by casting spells, changes the scene to a desert full of terrifying apparitions who carry Agilea away.

Act 4

The King is told by Arcane of how the witch Medea spirited Agilea away. The horrified Egeo swears she will be punished.

In the enchanted realm where Agilea is captive, Medea tells her she must agree to marry the King instead of Teseo, or the hero will meet his death. Medea shows her a vision of the sleeping Teseo, menaced by specters about to kill him. Agilea agrees to renounce him and marry the King instead to save Teseo's life, whereupon Medea transforms the scene to a paradisaical realm where Teseo hears Agilea's voice tearfully telling him she no longer loves him. Agilea's sorrow moves the heart of Medea who informs the lovers she will no longer attempt to part them, to the joy of Teseo and Agilea.

Act 5

Medea's sympathy for Teseo and Agilea's love did not last long; once again tormented by jealousy, she has convinced the King that Teseo is a threat to his throne and gives the King poison to put in Teseo's drink.

Teseo and Agilea enter with their friends, celebrating their marriage. The King offers to drink to their happiness and gives Teseo the poisoned drink to toast with in return. Teseo draws his sword to swear his loyalty to the King and is about to drink the poisoned beverage when the King recognises the sword as the one he had sent with his baby son years before so that he would be able to recognise him when grown up. The King dashes the cup from Teseo's hand and embraces him as his son. Not only will Teseo and Agilea now live in married happiness, Arcane and Clizia can marry too. The enraged Medea appears on a flying chariot drawn by fire-breathing dragons. Swearing vengeance, she orders the dragons to set the palace on fire, but the goddess Minerva descends from heaven, banishes Medea, and blesses the King, the two pairs of lovers, and Athens.