The witches Granny Weatherwax and Nanny Ogg visit the Ankh - Morpork Opera House to find Agnes Nitt and get caught up in a story similar to The Phantom of the Opera .
Agnes Nitt is a girl from Lancre .
The witches Granny Weatherwax and Nanny Ogg visit the Ankh - Morpork Opera House to find Agnes Nitt , a girl from Lancre , and get caught up in a story similar to The Phantom of the Opera .