To Titipu comes Nanki-Poo, son of the Mikado, who, to escape the attentions of Katisha, has fled his father’s court disguised as a second trombone player. He falls madly in love with Yum-Yum, who is already betrothed to her elderly guardian, Ko-Ko, and so their case seems hopeless. Wedding preparations are already in hand when a letter arrives from the Mikado announcing that unless someone is beheaded within a month the post of Lord High Executioner will be abolished and the city reduced to a village.

To avoid irretrievable ruin for everyone and after consultation with Pooh-Bah (who occupies every conceivable post from First Lord of the Treasury to Private Secretary - with appropriate salaries) it is decided that a victim must be found at once. The difficult choice is made when Nanki-Poo, overcome with grief at his inability to wed Yum-Yum announces his intention to commit suicide. Ko-Ko sees a way out and suggests to Nanki-Poo that he should allow himself to “be beheaded handsomely at the hands of the Public Executioner”. Nanki-Poo agrees on the condition that he shall marry Yum-Yum at once. Ko-Ko reluctantly assents for he realises that she will be a widow in a month and free to marry him. A flaw in this convenient arrangement is found: when a married man is beheaded his wife is buried alive!

In the midst of this dilemma the approach of the Mikado is announced. Matters are serious for Ko-Ko but his ready wit saves him. Why kill anyone when an affidavit that an execution has taken place will do just as well? Pooh-Bah, being grossly insulted, insists on a “cash down” settlement before he endorses the fiction.

The Mikado announces that he has come about a different matter namely the disappearance of his son from the Imperial Court. It is now discovered that the schemers have unwittingly sworn to the execution of the heir to the throne.

Ko-Ko saves himself and his accomplices from “death by boiling oil or melted lead” by calling Nanki-Poo (about to go on his honeymoon) back to life and sacrificing himself in marriage to Katisha who secures the reprieve. What a price to pay: poor Ko-Ko.