Act I. In the village of Rederring in Cornwall, a group of the world's only "professional corps of bridesmaids" are urging the heroine, "sweet Rose Maybud" to marry, as none of the young men of the village will marry anyone else until she does. They urge Dame Hannah to marry Old Adam Goodheart, the servant of prosperous young farmer Robin Oakapple, but she reveals that she has sworn to marry no-one since she found out that her true love was one of the Bad Baronets of
Ruddygore Ruddigore — who has died in agonies, as all the Baronets have all been cursed by a witch whom the first baronet burned to commit at least one crime a day or die if they don't do so. Disappointed, the maidens leave; Rose arrives, revealing to her aunt that she has feelings for Robin, but that she cannot ask him, since her book of etiquette, left to her by her dead mother, forbids her to speak until she is spoken to. Dame Hannah departs; Robin enters but cannot nerve himself to ask Rose to marry him. Meanwhile, his foster brother, Richard Dauntless, arrives home; Robin asks him to woo Rose for him — but when Richard sees Rose, he falls for her himself, and proposes. Rose, guided by her book of etiquette, accepts; but when Robin reveals that he also loves her — and is, by the way, far more faithful, far more sober, and far wealthier than Richard, Rose dumps the honest mariner and hooks up with Robin. Meanwhile, Mad Margaret, a village maiden driven mad by being loved and cast aside by Sir Despard Murgatroyd, the current Bad Baronet, knowing that his Bad Deed for the Day will be to carry off Rose Maybud, arrives, and hurries Rose away as Sir Despard and his "evil crew" of "Bucks and Blades"note arrive, greeted by the bridesmaids. Alone, Sir Despard reveals that he loathes the whole business of committing crimes, and longs to get out of it — when Richard enters, to reveal that Robin Oakapple is really — Sir Ruthven Murgatroyd, Despard's older brother and true Baronet of Ruddigore. They reveal this at Robin and Rose's wedding; Robin, as a "pure and blameless peasant," cannot deny it. Rose deserts Robin for Despard, but he, as "a virtuous person, now" decides to marry Mad Margaret — so Rose takes Richard, perforce. Robin falls senseless.
Act II. Robin, now a Bad Baronet, has been avoiding committing any real crimes by substituting extremely minor infractions. Even when Richard and Rose come to ask his consent to marry, he does not seize her, but yielding to her pleas, allows it and dismisses them. Meanwhile, Despard and Margaret arrive to urge him to repent (for the crimes Despard has committed!) and Robin agrees to do so. Such behaviour does not satisfy his ancestors, who come to life to demand that he commit a crime straightway, inflicting on him hideous agonies when he refuses. He consents, and commands Old Adamnote to "carry off a maiden – any maiden." Old Adam obligingly carries off Dame Hannah, who aggressively attacks Robin in defence of her virtue — rousing Sir Roderick, who rebukes him for carrying her off. Suddenly, Robin, by a brilliant stroke of logic, realizes that refusing to commit a crime a day is tantamount to suicide — but suicide is itself a crime! That being the case, Sir Roderick never should have died at all, and so comes back to life; he and Hannah are reunited; Robin and Rose are reunited; Despard and Margaret are (still) reunited; and Richard will have to make do with Zorah, the chief bridesmaid. All ends with a happy chorus.