Admeto, Rè di Tessaglia, HWV.22

Scene:Greece, in legendary times.

In a room of his palace, dominated by a statue of the god Apollo, King Admetus of Thessaly lies dying, tormented by terrible dreams. He is told by a courtier, Orindo, that his brother, Trasimede, is also in a bad way, obsessed with the portrait of a woman. The hero Hercules, on his never ending mission to perform glorious deeds to increase his fame, has come to pay a visit to his friend King Admetus. As her husband the king sleeps, his wife Alceste prays to Apollo to spare his life. The statue speaks and informs her that only if a close relative dies in his place will Admetus be permitted to continue to live. Alceste resolves to sacrifice her life for her husband.
Living in a nearby wood, disguised as shepherds, are Princess Antigona of Troy (which was burnt to the ground by Hercules) and her tutor Merapse. King Admetus had been betrothed to marry Antigona, but jilted her in favour of Alceste. This rejection of her is the reason, Antigona believes, why he is being punished with a mortal illness. She sends Merapse to the palace, instructing him to pretend that he is her father.
In the gardens of the palace, Alceste holds a dagger, preparing to die in her husband's place as she bids farewell to her grieving ladies-in-waiting, and then retires. Admetus, rejuvenated, enters with his friend Hercules, celebrating his recovery. Lamentations are heard from within and Admetus is horrified to see his wife's dead body. Admetus knows that Hercules once descended into the underworld and brought the hero Theseus back to the land of the living and asks him to do the same for Alceste, to which Hercules agrees.
Merapse returns to Antigona in the woods and tells her about Alceste's death and Admetus' recovery. They are glad that now there seems to be nothing in the way of Admetus making Antigona his wife, as he had promised. A hunting party approaches, led by Trasimede, who recognises Antigona as the woman whose portrait he carries about with him at all times, never ceasing to gaze at it. She insists, however, that he is mistaken; her name is Rosilda, she tells him, and the man with her is her father, called Fidalbo. Trasimede offers her a job at the palace, working as a gardener, which Antigona is glad to accept as she will be able to be close to Admetus that way and hopes to teach him a lesson.

The second act opens in Hades, where Alceste, tormented by the Furies, is chained to a rock. Hercules appears, fights with Cerberus the guard dog of hell, overcomes the Furies and breaks the fetters tying Alceste to the rock. She joyfully looks forward to being reunited with her husband.
Antigona is working at her new job as a gardener at the palace, where she has attracted the unwelcome attentions of the courtier Orindo, whom she spurns. Trasimede has lost interest in the portrait he was so obsessed with now he sees "Rosilda" who so closely resembles it, and tosses the portrait aside, whereupon Orindo picks it up. Antigona / "Rosilda" is not interested in anyone but King Admetus, however, and rejects Trasimede also.
Orindo takes the portrait to Admetus and tells him that Trasimede had not been honest when he had shown him another portrait of the Trojan princess he had been engaged to; Trasimede had obviously substituted a portrait of a far less attractive girl. Admetus is astonished by the resemblance of the portrait to his new gardener "Rosilda"; she tells him that Princess Antigona is dead and asks him if she were still alive, would he marry her. Admetus gives no satisfactory answer, leaving "Rosilda" still very unhappy.
In the woods, Alceste, returned to life, is now disguised as a male soldier, worried that her husband, thinking her dead, may have fallen in love with someone else or even married another woman. When she sees the lovely "Rosilda" working in the palace gardens, she worries her fears were well-founded.

Trasimede, madly in love with "Rosilda", has abducted her. Merapse tells Admetus who "Rosilda" really is and that she still loves the king. Hercules, not wanting to give Alceste's disguise away, tells Admetus that he was unable to find her in Hades. It seems to Admetus that his duty is now to marry Antigona.
Trasimede, feeling guilty about abducting "Rosilda", has released her. When the disguised Alceste sees "Rosilda" sighing over a portrait of King Admetus, she snatches it from her hand.
Admetus and Antigona make plans for their wedding, watched by the jealous Trasimede and Alceste in disguise. Trasimede decides to kill his brother but Alceste dashes his weapon from his hand, saving her husband's life. When Admetus realises Alceste has been restored to life, he is undecided as to the honourable course for him to take - should he return to his wife, whom he thought dead, or keep his pledge to Antigona? Antigona solves this dilemma for him by taking his hand and putting it in that of Alceste, telling the king to return to the woman who has now saved his life twice. Trasimede begs his brother for forgiveness, which is granted. Alceste rejoices once more in her husband's love.