Set in a pseudo Japanese locale known as Titipu, the town tries to insulate itself from the consequences of this law by appointing its biggest flirt, Ko-Ko, to the position of Lord High Executioner. Ko-Ko has a long list of potential victims, none real prospects, but the arrival of the "wand'ring minstrel" Nanki-Poo, in search of his beloved Yum-Yum - one of "3 little maids from school," all Ko-Ko's wards - provides a different opportunity.
Ko-Ko, now threatened with death himself for non-performance of duty, gets Nanki-Poo to agree to his own execution in return for being allowed one month of married happiness with Yum-Yum. A fearsome elderly lady named Katisha interrupts the celebration which greets this announcement, but no one pays any attention to her until she returns later with the Mikado himself. Ko-Ko panics when the Mikado's arrival is announced and begs Nanki-Poo to have his name forged on a death certificate for immediate release - in return for a permanent extension of his marriage. The Mikado is none too pleased when he discovers the name on the certificate, since Nanki-Poo is actually his son in disguise. But, in the topsy-turvy world of Gilbert & Sullivan, all is resolved with a pretty smile, a few clever words and the Mikado's pronouncement that "nothing could possibly be more satisfactory."