Act I

The act opens in the courtyard of Ko-Ko's palace in the town of Titipu. Ko-Ko, a tailor by trade, has recently been elevated to the rank of Lord High Executioner resulting in all of the State officials resigning in disgust. All of their offices and salaries have, however, been obligingly taken over by Pooh-Bah, a haughty but delightfully corruptible entreperneur. Ko-Ko is in love with his beautiful ward, Yum-Yum, but is not, however, her only admirer. The Mikado's son, Nanki-Poo, has fled his father's court to avoid being wedded to the ageing and dominant Katisha. Disguised as a musician in the Titipu Town Band, Nanki-Poo has come to find Yum-Yum, with whom he is in love, only to discover that Ko-Ko himself has plans to marry her that very day. Yum-Yum and Ko-Ko's two other wards, Pitti-Sing and Peep- Bo, arrive. Nanki-Poo succeeds in drawing Yum-Yum aside to confess his love. Whilst these flirtations are blossoming, Ko-Ko receives a letter from the Mikado enquiring why no execution has taken place in Titipu for a year and requesting this be remedied forthwith. Unable to find a volunteer, Ko-Ko is relieved to discover that Nanki-Poo is contemplating suicide on account of his unrequited love for Yum-Yum. Ko-Ko extricates himself from this predicament by striking a bargain with Nanki-Poo that the latter will allow himself to die at the hands of the Public Executioner after one month, provided that he is permitted to marry Yum-Yum immediately. In the course of the wedding preparations Katisha appears seeking her perjured lover Nanki-Poo. She recognises him and tries to reveal his identity to the townspeople, but protectingly they shout her down. Furious, she makes a dramatic exit vowing vengeance to reveal all to the Mikado.

Act II

The second act opens in Ko-Ko's garden with the wedding preparations of Yum-Yum and Nanki- Poo. Yum-Yum is reflecting how beautiful she is. Her sorrow at the thought of losing her young husband after only one month is, however, eclipsed by Ko-Ko's horrifying discovery that by law. when a married man is beheaded his wife must be buried alive. Nanki-Poo realises he must be honourable and release Yum-Yum to marry Ko-Ko, but whilst they are deliberating the Mikado arrives, with Katisha, looking for his long-lost son. Ko-Ko mistakenly concludes the Mikado has come to check that his decree concerning executions has been obeyed. Ko-Ko schemes to extricate himself once again - Nanki-Poo and Yum- Yum must marry and disappear. Ko-Ko bribes Pooh-Bah to issue a Coroner's Certificate confirming that Nanki-Poo has been executed. A vivid description of the 'execution' is given to the Mikado and all assembled by the three conspirators Ko-Ko, Pitti-Sing and Pooh-Bah. However, Katisha spots Nanki-Poo's name in the Certificate and the Mikado declares that the punishment for compassing the death of the Heir Apparent is immersion in boiling oil. All three conspirators are sentenced to death. There is only one way out - the unhappy Ko-Ko must marry Katisha, Nanki-Poo must return to life and the Mikado be placated. Katisha is successfully wooed by Ko-Ko's sad story of Tit Willow, Nanki-Poo is now safely able to reveal he is alive and has married Yum-Yum and 'nothing' declares the Mikado 'could possibly be more satisfactory'.