Un Ballo in Maschera

Act 1
Gustavus III, the King of Sweden, is secretly in love with Amelia, the wife of his faithful aide, Count Anckarstroem. When Anckarstroem warns him that a conspiracy is afoot, Gustavus is too preoccupied with his own thoughts of Amelia to be much concerned. The Minister of Justice enters and asks Gustavus to banish Mam'zelle Arvidson, a sorceress whom he considers a menace to the town. Gustavus decides to pay her a visit and draw his own conclusions. Hoping for a chance to carry out their assassination plan, the conspirators Count Horn and Count Ribbing join the excursion.
The group finds Mam'zelle Arvidson's dwelling filled with excited onlookers. Amelia's servant enters and asks Mam'zelle Arvidson for a private consultation for her mistress. The fortuneteller sends everyone away, and all leave except Gustavus, who stays in hiding. Amelia enters and begs for a potion to release her from her ruinous, secret passion for Gustavus. Mam'zelle Arvidson assures her all will be well if she drinks the juice of a special herb that she will find near the gallows.
The King's friends return and call for a prophecy. Gustavus asks Mam'zelle Arvidson to read his palm. She states that he will soon be killed by the next man to shake his hand. Gustavus jokingly offers his hand to his assembled friends, but no one will take it. At this moment, Anckarstroem arrives and Gustavus clasps his hand. The crowd proclaims the prophecy preposter­ous, since Anckarstroem is Gustavus's most trusted friend.

Act 2
Near the gloomy gallows, Amelia seeks the magic herb. She is interrupted by Gustavus. Knowing that this first secret encounter must be their last, Amelia confesses her love. As a man approaches, Amelia lowers her veil. It is Anckarstroem, who has come to alert his sovereign that the conspirators are nearby. Anckarstroem begs Gustavus to flee the assassins. Reluctant to desert Amelia, Gustavus makes Anckarstroem swear that he will conduct the lady to the city gates and not attempt to discover her identity. Gustavus escapes just in time.
Thwarted, the conspirators demand to see the face of the veiled woman. A struggle ensues, and, fearing her husband will be killed for his loyalty, Amelia drops her veil. The conspirators laugh, seeing that the woman is Anckarstroem's wife. Horrified, Anckarstroem asks two of the conspirators, Horn and Ribbing, to call on him the next day.

Act 3
Anckarstroem insists that Amelia must die. She begs for one favor: a chance to embrace their son. Her wish granted, Amelia leaves the room. Anckarstroem reconsiders his course of action and decides that Gustavus alone must pay. Ribbing and Horn keep their appointment and Anckarstroem joins their conspiracy. To settle who is to be honored with the assassin's task, they decide to draw lots. Amelia enters the room and Anckarstroem orders her to draw the lot.
Anckarstroem is chosen. In spite of a letter warning him of danger, Gustavus defies fate and attends a masked ball as planned. As the conspirators search the ballroom, Anckarstroem tricks Oscar, the King's page, into revealing the details of his master's costume. Amelia advises Gustavus to escape before it is too late. As they say goodbye, Anckarstroem steps between them and stabs Gustavus. Dying, Gustavus commands Anckarstroem's release. He tells the remorseful Count that his wife is innocent. The King's last words pardon all who conspired against him.