Un Ballo in Maschera
In the royal palace at Stockholm, King Gustavus III is in a difficult position. He has enemies, Counts Horn and Ribbing, who are plotting against him. And although he has a loyal friend in Count Anckarstroem, he nurses a secret love for Anckarstroem's wife Amelia, whose name he is overjoyed to see on the guest-list for a forthcoming masked ball.
More immediately, he is asked to approve the banishment of Ulrica, a gypsy fortune-teller accused of witchcraft, but decides it would be more entertaining to investigate her powers by paying her a visit. In disguise.
Arriving at Ulrica's hut dressed as a fisherman, Gustavus is surprised to find Amelia there, soliciting a cure for guilty love. Ulrica sends her off to make a potion out of herbs gathered at midnight by a gallows-tree.
Gustavus then steps forward and is told that he is to be murdered by the man who next shakes his hand. Gustavus laughs it off. And laughs still when the loyal Anckarstroem arrives, clasping his sovereign's hand in friendship.
Amelia is at the gallows-tree searching for herbs when she is interrupted by Gustavus. They declare their love for one another, he with ardour, she reluctantly; but there's no time to act upon it. Anckarstroem arrives to warn the King of a conspiracy to kill him. Thrown into confusion, Amelia hides her face and Gustavus entrusts this now heavily veiled woman to the protection of her unknowing husband before making a hasty escape. But then the truth emerges. Caught by the conspirators, Amelia's veil comes off and she's revealed as Anckarstroem's own wife – to the amused delight of everybody except Anckarstroem who, in his shame, curses Gustavus and decides to join the plot against him.
At home together, Anckarstroem threatens to kill Amelia for her unfaithfulness, but then decides the blame lies with Gustavus, who must die instead. With the enforced assistance of Amelia, the conspirators draw lots to determine who should carry out the murder. In fulfilment of Ulrica's prophesy it falls to Anckarstroem. And it will take place at the masked ball later in the day.
Meanwhile Gustavus, who knows nothing of all this, decides on the honourable course of distancing himself from Amelia. But hopeful of seeing her one last time, he ignores a mysterious letter warning him that his life will be in danger at the ball – which he duly attends, in a costume that makes him hard to identify. Anckarstroem nonetheless tracks him down. The inevitable happens. And as he dies, Gustavus not only assures Anckarstroem of Amelia's purity but pardons him for his act of predestined vengeance.