An early Boronet of Rudigore 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 legen to the 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 passsion. We now learn through Adam, an old retainer, that Robin is really Sir Ruthven (pronounced "Rivven") Mrgatroyd, 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 too 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 for 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 taht she had been in love with the present bad baronet, Despard. In a song, Despard reveals that depths of his infamy, but notes that he makes a point of atoning for every bad action by following it with a good once. 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 teh 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 now Rose, not at all abashed, once more falls back on Richard, and a Dance ends the first act.
In the gloomy Picture Gallery of Ruddigore Castle, teh 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 marrage. After some trouble, they obtain it, and depart. Robin them makes an impassioned appeal to his ancestors to relieve him of doing a daily crimie. Stepping down from their frames, and led by his uncle Roderic, they accuse hime 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" tehy have teh 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 hime a maiden - any maiden!
A reformed Despard and Margaret now appear, and soberly attired, and describe themselves as 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 none 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 teh excited entrance of Robin - he has the solution of the whole business. Pointing out that , as a refusal to fulfil the terms of teh Curse amounts to suicide, and as suicide is itslef a crime, it follow that theeCurse is inoperative! So Roderic finds that he must still be alive, Rose at once becomes the bride of a refomred Robin, Richard appropriates teh Chief bridesmaid, and all ends in general rejoicing.