A Rough Guide

Lots of folk pretend to be Japanese.  The formidable Katisha has claimed the Mikado's son Nanki-Poo (I'm not making it up) in marriage.  Terrified he has fled to Titpu (still not making it up) as a wandering minstrel.   Here he had fallen in love with Yum-Yum but (as ever) she is promised to Ko-Ko. 

Now, two things helpfully coincide: Nanki-Poo is looking to hang himself in grief and Ko-Ko receives a letter telling him that the Mikado has spotted there have been no executions in the town; this must be resolved or the town will be reduced in status to a village.

So, Nanki-Poo volunteers.  The scene is now set for the usual confusion and subterfuge.  Pretend executions etc...eventually Ko-Ko woos Katisha and, with her help, they all live happily ever after.