Act I

An early baronet of Ruddigore had a witch burned at the stake and she cursed him and all his line, dooming them to commit at least one crime a day, under penalty of dying in unspeakable agony. Dame Hannah narrates this legend to a chorus of professional bridesmaids, gathered around the cottage of Rose Maybud, an attractive young damsel who has not yet found a husband. Robin Oakapple, a young farmer, is in love with Rose, but is too bashful to declare his passion. We now learn through Adam, an old retainer, that Robin is really Sir Ruthven (pronounced "Rivven") Murgatroyd, the true Baronet of Ruddigore, who has fled from the curse, leaving it, with the title and estates, to his younger brother, Despard. His foster-brother, Richard Dauntless, who has just returned from sea, also knows Robin's true identity. Learning of the deadlock in Robin's love-affair, Richard volunteers to see the lady and clear up the situation. On meeting Rose, however, he falls in love with her, and as his guiding principle is to obey "the dictates of his heart," avows his love to her, and is accepted. But when Rose learns of Robin's love to her, she promptly transfers her affections to him, remarking that while Richard is a penniless sailor, Robin is a prosperous farmer.

Mad Margaret enters, and we learn that she had been in love with the present bad baronet, Despard. In a song, Despard reveals the depth of his infamy, but notes that he makes a point of atoning for every bad action by following it with a good one. Richard, still obeying the "dictates of his heart," reveals to him that his brother, Sir Ruthven, is alive, and is in this very village, masquerading as Robin Oakapple. Robin now enters with his promised bride and the chorus of bridesmaids to celebrate the nuptials. But the wedding is rudely interrupted by the revelation that Robin is really the bad baronet. Rose promptly offers herself to Sir Despard, who declares that he, being no longer the bad baronet but a virtuous person, will be true to Mad Margaret. So Rose, not at all abashed, once more falls back on Richard, and a dance ends the first act.

Act II - The House of Lords

The second act takes place in the gloomy picture gallery of Ruddigore Castle, where the portraits of his ancestors look grimly down upon a sadly changed Robin. Richard and Rose dance in with their train of bridesmaids to ask Robin's consent to their marriage. After some trouble, they obtain it, and depart. Robin then makes an impassioned appeal to his ancestors to relieve him of the necessity of doing a daily crime. Stepping down from their frames, and led by his uncle Roderic, they accuse him of evading the terms of the curse, and order him to do something really wicked - carry off a maiden that very day. When he refuses, they give him a sample of the "agonies" they have the power to inflict, and he is compelled to yield. The ancestors return to their frames, and Robin orders Adam to go at once and bring him a maiden - any maiden!

A reformed Despard and Margaret now appear, soberly attired, and describe themselves a district visitors engaged in charitable activities. They have come to implore Robin to forswear his wicked ways. He declares he will do so, when, upon their departure, Adam enters with the "maiden" he was sent to abduct. She turns out to be non other than the mature Dame Hannah, who proves so well able to protect herself that Robin has to call upon his uncle Roderic for help. Roderic steps down from his frame, and we learn that he and Hannah were once lovers. Robin is summarily dismissed and the reunited pair indulge in a sentimental duet. Their reunion is interrupted by the excited entrance of Robin – he has the solution of the whole business. Pointing out that, as a refusal to fulfil the terms of the curse amounts to suicide, and as suicide is itself a crime, it follows that the curse is inoperative! So Roderic finds that he must still be alive. Rose at once becomes the bride of a reformed Robin, Richard appropriates the chief bridesmaid, and all ends in general rejoicing.