What sort of person sits down and writes a maniacal laugh? And all those exclamation marks, you notice? Five? A sure sign of someone who wears his underpants on his head.

Opera can do that to a man . . .

It can also bring Death. And plenty of it. In unpleasant variations.

This isn't real life - it's worse. This is the Opera House, Ankh-Morpork . .

. a huge, rambling building where innocent young sopranos are being targeted by a strangely familiar evil mastermind in a mask and evening dress and with a penchant for lurking in shadows and occasional murder. But Granny Weatherwax, Discworld's most formidable witch, is in the audience.

And she doesn't hold with that sort of thing. There's going to be trouble (but nevertheless a good evenin's entertainment with murders you can really hum to) and the show MUST go on.
 
The Discworld novels can be read in any order but Maskerade is the fifth book in the Witches series.