A travesty of internet justice.

It appears that no one has ever written a Discworld/Petshop of Horrors crossover in which Count D sets up shop in Ankh-Morpok, becomes buddies with Sybil, and gets her to introduce him to individuals who might be interested in acquiring pets, while Vimes desperately attempts to connect him to the mysterious crimewave taking place.

Vetinari is unsupportive due to D's entirely appropriate admiration of Wuffles, and also probably because he once had some alarming arrangement with D's father. Everyone else in the Guard has, separately, been at some point seen to have brought D sweets at tea-time. Only a nonexistent talking dog is willing to help Vimes bring the Count to justice!

(For some reason I haven't figured out yet. Susan might be better, but I'm not immediately seeing how you'd get her into the shop. She's arguing with the Death of Rats while he's on his way over there, maybe.)