For episode 23, Elizabeth and Ben are joined by opera singer Myf Coghill on a trip to Ankh-Morpork's opera house in Terry Pratchett's 1994 Discworld novel of witches, phantoms and experimental cookery: Maskerade!

Nanny Ogg's coven with Granny Weatherwax is short a witch. She decides young Agnes Nitt - last seen dabbling in the craft while wearing black lace and calling herself “Perdita” - is just the person to fill the position. But Agnes has run off to Ankh-Morpork and joined the opera, where a mysterious “Opera Ghost” has turned from good luck charm to demanding, dangerous and possibly deranged. Can “Perdita” find out the identity of the Opera Ghost before the bodies start stacking up - and before Granny and Nanny stick their noses in and do it for her?

Pratchett delves into a world hitherto unknown to him and takes Granny and Nanny to the big city for their penultimate book, heavily influenced by The Phantom of the Opera, and about much more earthly matters than their previous adventures. We learn a lot about opera, Andrew Lloyd Webber and the world of publishing, and delve into Pratchett's treatment of Agnes, a beloved character whose unflattering portrayal was the subject of many questions and comments.

Did Maskerade bring out the opera fan in you? Do you think Agnes deserved better? And despite being a bit of a downer, is this one of the best Discworld books we've discussed so far? Use the hashtag #Pratchat23 on social media to join the conversation and let us know what you think!

Guest Myfanwy Coghill is an opera singer, soon-to-be qualified teacher, and Dungeon Master (of the Dungeons & Dragons variety). You can follow her on Twitter at @_merlenoir_.

You'll find the full notes and errata for this episode on our web site.

We're staying in Ankh-Morpork for Feet of Clay in October before heading back in time to explore the origins of Granny Weatherwax in November with Equal Rites. Plus our subscriber-only bonus podcast, Ook Club, has launched! You can subscribe for as little as $2 a month to check it out. You'll find all the details on our Support Us page.