The first time Demeter warns about Macavity, it seems like a false alarm, as it's only Mungojerrie and Rumpleteazer...who work for Macavity. She smelled him on them!
Macavity, He's broken EVERY human law? HMM... Just how literally do they mean EVERY?
Especially as some would be bloody hard for a cat... how, for example, would a cat commit white collar crimes?
Simple. Macavity is JUST THAT DAMNED GOOD.
It's not exactly horror, but Mungojerry and Rumpleteaser breaking a Ming vase, one of the rarest most expensive bits of pottery in the world... It's a surprise they haven't been thrown out of the house...