The show opens in the town of Titipu where the chorus of nobles are joined by Nanki-Poo, disguised as a second trombone, who is looking for Yum-Yum, the ward of Ko-Ko. A noble lord named Pish-Tush asks what Nanki-Poo's business is with Yum-Yum, and learns that the minstrel had seen the girl a year ago when he was a member of the town band, and they had fallen in love. But Yum-Yum was betrothed to her guardian Ko-Ko, 'a cheap tailor.'
However on learning that Ko-Ko was condemned to death for flirting, the minstrel has hurried back to try to claim Yum-Yum. Unfortunately on his return he finds that far from being dead, Ko-Ko has in fact been let out on bail, and appointed Lord High Executioner. There is worse to come as Pooh-Bah, who holds every major office of state, informs Nanki-Poo that Yum-Yum and Ko-Ko are to be married that very day.
One of the best loved, most popular of all Gilbert and Sullivan's operettas.