Act I is laid in a fortress near Plymouth, held by _Lord Walton_ for

Cromwell. _Lord Walton's_ daughter, _Elvira_, is in love with _Lord Arthur Talbot_, a cavalier and adherent of the Stuarts, but her father has promised her hand to _Sir Richard Forth_, like himself a follower of Cromwell. He relents, however, and _Elvira_ is bidden by her uncle, _Sir George Walton_, to prepare for her nuptials with _Arthur_, for whom a safe-conduct to the fortress has been provided.

_Queen Henrietta_, widow of Charles I., is a prisoner in the fortress. On discovering that she is under sentence of death, _Arthur_, loyal to the Stuarts, enables her to escape by draping her in _Elvira's_ bridal veil and conducting her past the guards, as if she were the bride. There is one critical moment. They are met by _Sir Richard_, who had hoped to marry _Elvira_. The men draw their swords, but a disarrangement of the veil shows _Sir Richard_ that the woman he supposes to be _Lord Arthur's_ bride is not _Elvira_. He permits them to pass. When the escape is discovered, _Elvira_, believing herself deserted, loses her reason. Those who had gathered for the nuptials, now, in a stirring chorus, invoke maledictions upon _Arthur's_ head.