A reception hall at the Governor’s house in Boston. Even as the good deeds of Riccardo, governor of Massachusetts, are loudly acclaimed by all, Samuel and Tom, the ringleaders of an opposition party, murmur threats of rebellion and contemplate his assassination. The page Oscar steps forward with a list of guests invited to the masked ball which the governor has decided to give. One of the names on the list is Amelia, wife of Riccardo’s secretary and loyal friend, the Creole Renato. Riccardo is in love with her and since he cannot openly show his feelings he gives himself up to private dreams of love. When everybody has gone out, Renato enters and notices the perturbed look on Riccardo’s face. The governor is afraid his friend may have read his heart. But Renato is concerned only for his master’s life, having found out that Samuel and Tom are plotting against him, and he believes that Riccardo himself must have heard about this conspiracy. As if relieved to get a weight off his mind, the governor does not want to know the names of his enemies and refuses to consider any danger to himself. Renato urges him not to listen only to the voice of his own generous heart. At this point a judge enters and submits to the governor’s attention an order banishing Ulrica, a fortune teller «with unclean negro blood in her veins». But Oscar quickly comes to the woman’s defense and praises her gifts of divination and asks for her acquittal. Unsure of what action to take, Riccardo invites all those present to gather, suitably disguised, at the fortune teller’s hut to judge for themselves the quality of her arts in action. All except for Renato, who is worried about the danger his master may incur, receive the bizarre idea with amusement.
Observed by an awe-stricken but fascinated audience, Ulrica evokes the spirits of the deep. In the meantime, Riccardo is the first to reach the scene, disguised as a fisherman. From a concealed position, he watches the arrival of a sailor, named Silvano, to whom the fortune teller prophesies promotion in the near future and a prize of money in reward for faithful service. Riccardo is amused by this information and slips into the sailor’s pocket a piece of paper announcing his promotion, thus causing the witch’s prophecy to come true. But a servant now announces the entry of Amelia. Greatly agitated, she asks the woman to free her from the passion of love that is tormenting her. Ulrica prescribes a magic herb, to be sought and picked at midnight in a field where the gibbet stands. Despite her terror, Amelia resolves to go to that sinister spot. But Riccardo has heard all and is ready, now that he knows that she loves him, to follow her. Oddly disguised, Oscar, Samuel and Tom now burst into the hut accompanied by the whole of the governor’s retinue. Riccardo asks the woman to tell him his future, but her words are grim: for he shall soon be slain by a friend and the assassin will be the first person to shake him by the hand. With ostentatious hilarity, the governor attempts to exorcise this dire prophecy. And the entry of his deeply devoted friend Renato, who warmly shakes his master’s hand, reassures everybody. The oracle must surely have lied . Riccardo now reveals his true identity and revokes the fortune teller’s banishment while the people acclaim him.
Amelia arrives to a solitary field outside Boston, looking deeply shaken. She cannot bring herself to pick the herb that will rid her heart of all her passion for Riccardo. The latter now suddenly appears, and seeks to calm her. Eventually they confide their mutual love, but also the remorse caused by their guilt. But then, as unexpected as lightning, Renato arrives, searching for his friend to save him from imminent ambush by conspirators. Having covered her face with a veil just in time, the woman exhorts Riccardo to escape but the governor hesitates, refusing to leave without her. Then he makes up his mind to leave, but first entrusts the veiled woman to Renato, who promises to escort her to the city without ever speaking to her or looking at her. Both the conspirators are astonished to find Renato instead of the governor. Samuel declares that he wants at least to see the face of a beauty so compelling as to drag Renato out of town to such a sinister spot. Renato objects, and when Amelia sees her husband fall beneath the conspirators’ blows, she rushes to his defense and drops her veil in the process. Renato is flabbergasted, Amelia desperate and the conspirators amused. Pulling himself together, the governor’s secretary decides to get his revenge and accordingly invites Samuel and Tom to come to his house the next morning.
In a study in Renato’s house, he informs Amelia that she must die to wash away her infamous sins. She asks permission to embrace her son for the last time. Renato takes pity on her, realising that it is not her that he must harm, but the man who has betrayed his long and loyal friendship. The conspirators now enter and Renato sides with them. It only remains to decide who shall kill Riccardo. After casting their three names (Samuel, Tom and Renato) into a vase, they draw lots and Amelia herself is appointed to carry out the macabre task, her innocent hand having drawn precisely the name of her own husband, who exults with joy at his approaching revenge. A t that moment Oscar arrives with the invitations for the masked ball, which will afford the ideal setting in which to commit the deed.
In the meantime Riccardo, in his study, has taken the painful decision never to see Amelia again, and has signed a decree promoting Renato, who is to be accompanied by his wife, to a new post abroad. But still he cannot shake off his memories of Amelia. From behind the scenes can be heard the music of the masked ball which must have already begun. Oscar enters and hands Riccardo a note, warning him not to attend the ball, for it is known that an attempt on his life will be made there. Determined not to show cowardice in the face of danger, but most of all in order to see Amelia for the last time, the governor decides to go to the ball.
The festivities are in full swing with music and dancing and a throng of guests. Renato tries to get Oscar to tell him what costume the governor is disguised in. The page reveals Riccardo ’s identity to him. Meanwhile Amelia has recognized Riccardo and beseeches him to save his life. He tells her that she and her husband are to go to England and that this is their last farewell. But Renato now approaches and, to everyone’s dismay, stabs Riccardo. Before dying, the governor declares Amelia’s innocence and forgives all.
