Verity's old tabby cat Mabel might not be quite as lively as she used to be and yes, she smells a bit and doesn't always make it to the litter tray on time, but she really loves her. More importantly, Mabel once belonged to Verity's mum--not that Verity actually ever knew her mum because she died. She really doesn't mind too much about not having a mum, apart from when she goes to visit her grave, which makes her think about being in the ground with a head full of worms.
So when she finds Mabel dead in the wardrobe, it seems to Verity that it would be much better to take a few lessons from the ancient Egyptians: rather than bury the poor old thing she decides to mummify her so they can be together forever. But what with the problems involved in finding the mummification materials and the fact that Gran would probably fuss about hygiene if she knew anything about it, things don't quite go as planned.