Act I

Richard, Count of Warwick, English governor of Massachusetts, receives visitors in his residence. Among his court officials who praise their governor are Samuel and Tom who connive to murder Richard. Oscar, the page, brings Richard a list of invitations to a ball; it includes the name of Amelia, whom Richard is secretly in love with despite her being married to his friend and secretary, Renato.

When petitioners leave, Renato comes and warns Richard of a plot against him. He wants Richard to be cautious, but the Count refuses to arrest the conspirators or even to learn their names. The Supreme Judge comes with a proposal to expel Ulrica the fortuneteller. Oscar makes a passionate speech in her defense, and Richard decides to visit Ulrica himself. He invites his court to join him and have fun in disguise.

Ulrica invokes the Devil before the credulous folk. Questioned by the sailor Silvano, she predicts him promotion and rewards. Amid general exultation, the prophecy turns out to be true, since Richard had slipped money and a nomination order into the sailor's fortuneteller sends all the others out, while Richard hides himself to eavesdrop. Ulrica counsels Amelia, who seeks get rid of a sinful passion, to go to the sinister execution grounds, where she will find an herb of forgetfulness. When she leaves, Richard, disguised as a fisherman, requests a divination for himself. Ulrica predicts that he will die soon, murdered by the first one who shakes his hand. It happens to be the newly arrived Renato, which makes the courtiers disbelieve the prophecy. The grateful Silvano summons the people to sing Richard’s glory.

Act II

Amelia goes to pick the magic herb in the night and is followed by Riccardo who declares his love for her; Amelia tries to resist, but he makes her confess her own feelings: she too loves him. Richard rejoices, while Amelia is disconsolate. Renato intrudes: he is just a few steps ahead of the conspirators who are coming to kill Richard. Unrecognized by her own husband under her veil, Amelia together with Renato convinces Richard to run away. He asks Renato to care about his lady respecting her incognito, and leaves disguised in Renato’s clothes. The conspirators arrive to find a wrong victim and start pestering Amelia. Renato tries to protect her. In the confusion that follows, Amelia's veil falls. The husband is mortified and angry, Samuel and Tom laugh at the dumbfounded husband. Renato makes an appointment to meet the conspirators the next day.

Act III

At home Renato threatens to kill Amelia for her supposed infidelity. She pleads to be allowed to see their son for the last time. Moved to pity, Renato decides to satisfy his anger by killing the friend who betrayed him. When Samuel and Tom arrive, he asks to join their conspiracy. All three compete to carry out the murder and cast lots. Renato makes Amelia, unaware of their plot, to draw the lot for them. The lot has Renato’s name.

Oscar arrives with the invitations for the masked ball which is gleefully accepted by Renato. The conspirators hope to take advantage of the occasion and kill Richard. Amelia tries to think of a way to save the Сount without betraying her husband.

Richard signs an order that is to make Renato return to England with Amelia. His mind is full of ill forebodings. Oscar brings him an anonymous letter urging him to forego the ball for his own safety, but the Count despises the danger and proceeds to the feast.

At the ball, Renato makes Oscar reveal Richard’s disguise. Meanwhile, masked Amelia implores Richard to flee. He recognizes her and and informs her of the parting he had arranged. As they say their last farewell, Renato strikes Richard down. The assassin is capcaptured, but Richard, dying, proclaims Amelia innocent and pardons all the conspirators.