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.

The story begins with Agnes Nitt leaving Lancre to seek a career at the Opera House in Ankh-Morpork. When Granny Weatherwax realizes Nanny Ogg has written an immensely popular cookbook but has not been paid by the publisher, the witches also leave for Ankh-Morpork to collect the money, as well as to attempt to recruit Agnes into their coven, to replace Magrat Garlick who left the coven when she became Queen of Lancre (in Lords and Ladies).