In 17th-century England, the Civil War is raging between the republican Roundheads and the royalist Cavaliers. The Stuart King Charles I has been executed by the Roundheads under the leadership of Oliver Cromwell.

Act One
The belligerent Puritan Roundhead troops are girding themselves for a new day. From the chapel in the Roundheads’ stronghold, morning prayers can be heard. It is the day on which Elvira, daughter of the Governor, Lord Walton (Valton), is to celebrate her wedding. Walton has promised his daughter’s hand to his best officer, Richard (Riccardo) Forth. Elvira, however, is in love with Lord Arthur Talbot (Arturo Talbo), a supporter of the enemy royalists.

Elvira’s beloved uncle, Sir George (Giorgio), Lord Walton’s brother, brings the good news that he has persuaded Elvira’s father to allow her to marry her great love Arturo, rather than the Puritan Riccardo. Elvira, who had feared she would be forced to marry Riccardo, is beside herself with joy.

The despondent Riccardo is deeply disappointed that he may not marry Elvira, although she had been promised to him. Even his fellow officer, Bruno, who reminds him of his honour as a soldier, cannot lift his depression.

The Puritans welcome the bridegroom Arturo and hail the bridal couple. Arturo tells Elvira how happy their marriage will make him.  The wedding guests give the loving couple their blessing.

Lord Walton declares that he will unfortunately be unable to attend his daughter’s wedding, as he must immediately take an important prisoner before Parliament to be sentenced. While Elvira withdraws to prepare for the wedding, Arturo remains behind alone with the prisoner for a moment. He makes it known that he is a royalist supporter, whereupon the lady reveals her true identity: Henrietta Maria (Enrichetta), widow of the executed King Charles I. Arturo vows to save her from certain death on the scaffold.

Elvira is happy in her wedding dress. She asks Enrichetta to put on her veil, and the prisoner gladly complies. For a brief moment, Enrichetta is once more alone with Arturo, who seizes the opportunity to escort the endangered Queen, unrecognised under Elvira’s veil, out of the castle.

Riccardo, who will not accept that Elvira is to marry an enemy royalist, bars the supposed bridal couple’s path. He challenges Arturo to a duel. Enrichetta stands between them and lifts her veil. Having recognised her as the prisoner, Riccardo allows the two of them to escape. Elvira and the wedding party, who are looking for Arturo, discover that he has fled with the prisoner. The Puritans helplessly watch as the traumatised Elvira becomes increasingly disturbed.

Act Two
Giorgio and the Puritans deplore Elvira’s derangement: like a ghost, she aimlessly wanders about, begging for mercy, acting out the wedding ceremony, and constantly calling for Arturo. All the onlookers fear that Elvira will die of grief. Riccardo declares that Parliament has sentenced Arturo to death. The people demand vengeance for Elvira’s suffering and a harsh punishment for Arturo.

Memories and hallucinations merge in Elvira’s consciousness.

Giorgio is convinced that only Arturo’s return can save Elvira. He implores Riccardo to forgive his rival, to spare his life and thus to preserve Elvira from dying of lovesickness. Riccardo insists that Arturo be sentenced to death and that he deserves just punishment. Nonetheless, Riccardo is moved by Giorgio’s pleas. The pair assure one another emphatically that they will fight side by side for the fatherland, honour and freedom.

Act Three
Following his escape, Arturo has secretly returned to England, although he remains a fugitive. He hears Elvira singing a song of a wistful troubadour that he once wrote for her. Deeply moved, he sings the song himself. Elvira recognises his voice, and they are joyfully reunited. Elvira learns that Arturo still feels profound love for her, and that he abandoned the wedding only in order to save the life of the imprisoned Queen.

Riccardo and his soldiers discover Arturo and take him prisoner. The soldiers demand that he be executed forthwith; Giorgio and the women, on the other hand, beg that Arturo be pardoned. A fanfare is heard, heralding the news that the royalists have suffered a devastating defeat. A general amnesty has been declared for all prisoners. The Puritans celebrate their victory and England’s liberty. An ecstatic Elvira declares that she will love Arturo for all eternity.