A masked ball is due to take place at the palace of the governor of Boston, Riccardo, Count of Warwick. Oscar, the latter's page, presents his master with a list of the invited guests. Riccardo is delighted to see on it the name of Amelia, wife of his secretary, Renato. The count has fallen in love with the wife of his closest and most faithful friend. Renato has recently discovered a conspiracy against the Governor, but as yet has been unable to learn the names of the conspirators.

A judge is announced who brings for the Governor's signature a sentence of banishment from Boston of an old fortune-teller, by name of Ulrica. Oscar, however, intercedes for the fortune-teller. Riccardo decides to visit Ulrica in disguise and to put her powers of prophecy to the test.

Riccardo, Count of Warwick, enters Ulrica's hut disguised as a fisherman. Amelia, who has also come to consult Ulrica, is present too. Riccardo overhears Amelia ask Ulrica for a magic herb to cure her of her sinful love for Riccardo and thus put her out of her misery. Ulrica tells Amelia that she knows of such a herb but that she must pluck it herself, outside the city, at midnight. Once Amelia has departed, Riccardo asks Ulrica to tell his fortune. Ulrica tells him that he will die at the hands of a friend.

Who will be the slayer?È, asks Riccardo. ÇWhoever first shall shake your handÈ, Ulrica replies. At this moment, Renato enters and greeting the Count, shakes him vigorously by the hand. Riccardo laughs at the evil prophecy.

ACT TWO

Midnight. Amelia, deeply veiled, comes to pluck the magic herb. Riccardo arrives too to protect his sweetheart in case of danger. This unexpected meeting so disconcerts Amelia that she is unable to conceal from the Count her feelings for him. Footsteps are heard and Renato appears out of the darkness. Concerned for the safety of his master and, unbeknown to the latter, he has followed him. The conspirators are lying in wait for the Count not far away. He must leave immediately for his life is in danger. Renato does not recognize Amelia and Riccardo asks his secretary to escort the deeply veiled woman back to safety. But, on no account, is he to try and learn who she is. The Count himself returns to the city by a path known to him alone. Before Renato and his companion are able to make their escape, they are surrounded by the conspirators. The latter are astonished to see before them not the Count, but his secretary. They want to learn who the Governor's sweetheart is and force Amelia to lift her veil. Seeing his wife, Renato is overcome by rage and he now joins the conspiracy against Count Riccardo.

ACT THREE

Not wishing to bring disgrace upon his family, Renato refrains from his initial intention of killing his wife. He chooses for her a punishment far worse than death. Without knowing it, she will pick the murderer of the man she loves. When the conspirators draw lots to determine who is to kill Riccardo, Renato calls in his wife and commands her to draw a piece of paper from an urn. Amelia does as Renato asks, and pulls out a piece of paper with her husband's name on it. Renato is to kill the Count. He decides to do this at the masked ball to be held at the Governor's palace.

Not wishing to dishonour the name of his closest friend, Riccardo decides never to see Amelia again. Renato, accompanied by his wife, will be sent as ambassador to England.

The masked ball is in full swing.

The huge crowd of guests, wearing masks, whirl about the dance floor. Overcome by feelings of fear and apprehension, Amelia recognizes Riccardo under his disguise. She warns him that his life is in danger and begs him to leave the ball and go into hiding. For the last time, farewell, AmeliaÈ, Riccardo bids her. Accept my farewell tooÈ, Renato cries as he steps between them and stabs Riccardo.

The dying Riccardo forgives his murderer. He assures Renato that Amelia is innocent. These are his last words.