Plymouth, England, during the Civil War.
Charles l's widow, Queen Henrietta (Enrichetta), is being held captive in a fortress governed by the Puritan Lord Walton. His daughter Elvira loves Lord Arthur (Arturo) Talbot, a Cavalier. Although they are given permission to marry, Elvira is secretly loved by the Puritan enemy of Arthur, Sir Richard (Riccardo) Forth. Arthur helps the widowed queen to escape by dressing her in Elvira's bridal veil. Elvira, believing she has been betrayed, loses all reason.
Lord Walton's brother George (Giorgio) enters with news of Elviras ravings. He s followed by Richard, who announces that Arthur has been sentenced to death by Parliament.
The mad Elvira arrives, singing of her lost love. George urges Richard to save Arthur's life, for if he and Elvira are not soon reunited, she will surely die.
Richard reluctantly agrees, but swears that, should Arthur join the Royalist ranks in battle the following day, he will exact revenge for the pain Arthur has caused Elvira.
Arthur, though aware of the danger, returns to Elvira. They embrace, but Elvira, terrified that he will again disappear, cries out.
Her screams bring Richard and a group of Puritan soldiers to the scene. Richard pronounces Arthur's death sentence, but this brings Elvira back to her senses and the two are united for what seems the final time. At the last minute, soldiers announce the Stuarts' defeat and the end of the war. A universal pardon is issued, leaving Arthur aand Elvira free to marry.