Read the synopsis of Verdi's Un ballo in maschera.
Several officials are waiting for Gustavo, among them a group of conspirators led by Horn and Ribbing. Gustavo arrives and examines the list of guests for the coming ball. He’s elated to see the name of his secret love – Amelia – but is embarrassed when interrupted by her husband, Anckarström. He is Gustavo’s friend and advisor, and warns him of a conspiracy.
Gustavo refuses to listen. A judge arrives demanding the expulsion of the fortune-teller Madame Arvidson, but Oscar, Gustavo’s aide, defends her. Gustavo decides to witness the ‘witchcraft’ for himself, and proposes they go to see her work incognito.
Gustavo arrives at Madame Arvidson’s before the others. She prophesies wealth and status to Cristiano. Gustavo ensures her prediction comes true by slipping a commission, unseen, into Cristiano’s pocket. The crowd marvels at her powers, but are asked to leave when Arvidson agrees to meet a secret visitor. Gustavo hides, and is shocked to see Amelia creep in.
She wants respite from a secret love which is torturing her and is advised by Arvidson to find a drug which will help her forget her illicit passion. Astonished by Amelia’s revelation, Gustavo, still hiding, vows to be with her when she goes to get the drug.
Amelia slips away and the others arrive, including the conspirators. They wait as the disguised Gustavo has his own
fortune told. Arvidson correctly identifies him as a man who has ‘lived under the star of Mars’, but refuses to say any more.
When pushed by Gustavo, she finally relents and tells him he will be killed by the man who next shakes his hand. The crowd refuses Gustavo’s outstretched hand, but when Anckarström enters he shakes his friend’s hand. Gustavo dismisses the prediction as absurd, and removes his disguise. The crowd is amazed to see Gustavo amongst them, while Horn and Ribbing rue another missed opportunity to assassinate him.
Amelia has ventured out alone to get the drug that Arvidson told her about. She is surprised by Gustavo, who declares his love for her. Unexpectedly Anckarström appears. Amelia hurriedly covers her face, while her husband warns Gustavo of imminent danger and urges him to flee. As he escapes, Gustavo urges his friend to escort the veiled woman back to town without asking her identity.
The conspirators appear and confront Anckarström. In the struggle, Amelia’s veil drops and upon seeing her, Anckarström accuses his wife of infidelity. He asks Horn and Ribbing to meet him later.
Anckarström has resolved to kill Amelia but she protests her innocence, begging to see their child one last time. Anckarström relents, privately declaring that is it Gustavo, not Amelia, who should die. Horn and Ribbing arrive, and Anckarström vows to join their plot. All three want the prize of killing Gustavo. To resolve the matter, they agree to cast lots and call Amelia to draw the ‘winning’ name – Anckarström. Oscar arrives with invitations to the ball. Horn, Ribbing and Anckarström agree this is where the assassination will take place.
Torn between love and duty, Gustavo has resolved to announce his love for Amelia, and send her and her husband on a foreign posting. Oscar brings an anonymous note warning that an attempt on his life will be made at the ball. At the party, Anckarström tries to learn from Oscar which costume Gustavo is wearing. At first the aide refuses, taunting Anckarström, but finally answers. Meanwhile, Gustavo identifies Amelia and tells her of the decision he has made. As they say goodbye, Anckarström attacks. Fatally wounded, Gustavo insists that Amelia is innocent.