During the English civil war of the 1640s, Oliver Cromwell and his parliamentary forces (the Roundheads and the Puritans) fought to oust the Royalists (followers of the Stuart monarchy, also known as the Cavaliers). Before the opera opens, King Charles I has been executed, and his wife, Queen Enrichetta, has escaped.
ACT I
A castle in the south of England. Elvira and her family are followers of Cromwell. Elvira's father, Lord Gualtiero Walton, has promised her hand in marriage to the Puritan colonel, Sir Riccardo Forth, but she has fallen in love with a Royalist, Lord Arturo Talbot. As festivities begin in celebration of Elvira's wedding, Lord Walton unexpectedly agrees that Elvira may marry Arturo although he has yet to tell her. Riccardo laments Walton's decision and vows to thwart Elvira's marriage to Arturo. Shortly thereafter, Elvira and her uncle, Giorgio, are alone together. Elvira tells her uncle that she would rather die than marry Riccardo. Giorgio reassures her that he has convinced her father to let her marry Arturo. Elvira is ecstatic and as heralds proclaim the arrival of her suitor, she expresses her joy. The crowd wel¬comes Arturo, who brings gifts including a magnificent bridal veil, and their love is celebrated.
Elvira's father Lord Walton explains that he has to escort a female prisoner to London, and so cannot attend his daughter's wedding celebration. Everyone leaves but Arturo and the "prisoner," who reveals to Arturo that she is Enrichetta, the widow of the executed Charles I. Arturo, as a Royalist, pledges to help her escape. Elvira rushes back, joyously anticipating her wedding and showing off her wedding veil.
Elvira places the veil on Enrichetta to admire it, and then leaves when the guests call her to another part of the castle. Arturo decides to use the veil to smuggle Enrichetta away from the castle. As they are about to rush away, Riccardo appears and stops them, determined to kill his rival. Enrichetta reveals her identity to Riccardo who then lets them escape, knowing this will ruin Arturo. When Elvira and her friends return, Riccardo delightedly tells everyone Arturo has fled with the mysterious prisoner. Soldiers are sent to capture the traitors. Elvira, believing herself betrayed, loses her reason.
ACT II
The Puritans lament Elvira's madness. Riccardo arrives and reveals that Arturo is condemned to death in absentia. Elvira enters, utterly distraught, hallucinating, and inconsolable in her sadness. Giorgio tries to make Riccardo understand that Elvira will die unless Arturo is found and pardoned. Riccardo reluctantly agrees to renounce his love as Giorgio joins him in a promise to devote themselves to their country, victory, and glory.
ACT III
Arturo returns, eluding the Puritan soldiers, determined to explain himself to Elvira. When Elvira recognizes his voice, her reason is restored and she rushes to him. They express their ecstatic happiness.
Hearing the drums and imagining Arturo will forsake her again, Elvira slips back into madness and calls for the guards. They arrest Arturo and Riccardo declares that the sentence of death will be carried out. Arturo bids farewell to the now devastated Elvira. Just as the execution is about to take place, word conies that the Royalist forces are defeated, and there is a general amnesty. Arturo is saved; Elvira is restored to sanity, and the opera ends in general rejoicing.