I Puritani by Vincenzo Bellini

Set during the English Civil War, The Puritans is a story of love and seeming betrayal across family, religious and political lines. Charles l's widow, Queen Henrietta is imprisoned in a fortress governed by the Puritan Lord Walton. Despite the politics of the time, his daughter Elvira is betrothed to a Cavalier, Lord Arthur Talbot. When Arthur helps the queen escape, disguised in Elvira's bridal veil, Elvira goes mad, believing herself betrayed.

Elvira’s uncle, George, brings news of Elvira’s descent into madness. Sir Richard Forth, a Puritan who also loves Elvira, announces that Arthur has been sentenced to death by Parliament. Elvira arrives, lamenting her lost love. George urges Richard to save Arthur's life for Elvira’s sake. Richard concedes reluctantly, but nonetheless they agree Arthur will face death should he take part in battle the next day, as they will fight side by side for their cause.

Arthur seeks out Elvira, who is still distraught that he may desert her again. Richard arrives with a group of Puritan soldiers and pronounces Arthur's death sentence. Elvira is restored to sanity, united with Arthur in what seem to be their last moments. However, the end of the war is declared and a universal pardon proclaimed, leaving Arthur and Elvira free to marry.