The Opera House, Ankh-Моrpork...а huge, ramblin building, where innocent young sopranos are lured their destiny by a strangely-familiar evil mastermind in a hideously-deformed evening dress...
At least, he hopes so. But Granny Weatherwax, Discworld's most famous witch, is in the audience. And she doesn't hold with that sort of thing.
So there's going to be trouble (but nevertheless a good evening's entertainment with murders you can really hum...).