(TRG spoilers below the cut)
‘Corm said you’d need two or three outfits?’ ‘Ideally,’ said Robin. ‘I promise I’ll be very careful with them.’ ‘Oh, don’t worry about that, I’ve got far too many clothes… it’s my weakness,’ Prudence admitted, with a guilty smile. ‘Sylvie’s just got old enough to start borrowing stuff I can’t get away with any more, so I’m kind of hanging off giving it all to charity. What size shoes do you take?’ ‘Six,’ said Robin, ‘but—’ ‘Perfect. Same as me.’ ‘—you really don’t have to—’ ‘If you’re trying to look wealthy, accessories count,’ said Prudence. ‘Quite exciting really, helping someone go undercover. (...)’ - The Running Grave, Chapter 9
Just realised that Robin going undercover in the cult is a reverse Cinderella, with Prudence as fairy godmother, Mazu as evil stepmother and Strike's BMW's as the pumpkin carriage.