In a small Japanese town, Ko-Ko is appointed to the unenviable position of executioner. Knowing he must successfully perform before the appearance of the Mikado in a month's time, Ko-Ko finds a suitable victim in Nanki-Poo, who is distraught over his unrequited love for the maiden Yum-Yum. Nanki-Poo agrees to sacrifice his life if he is allowed to spend his remaining days with Yum-Yum, who is betrothed to Ko-Ko.

The Baronet of Ruddigore, Sir Despard Murgatroyd, has inherited a family curse which forces him to commit a crime every day — or die in agony. He hates the curse, doing his heinous misdeeds as early as possible and good works for the rest of the day to compensate!