While this is a fun story, it is, unfortunately, something of a historical urban legend. There are absolutely no written records of mass killings of cats, first off. Even if they did occur, they had little to no impact on the death rate from the plague- in China, India, Central Asia, and the Middle East the death rates were just as high- and there definitely weren't any mass cat killings there, since the writ of the Catholic Church didn't extend that far.@renxoarg
These days, most historical research leans towards the idea that the Black Death was kicked off and exacerbated by the end of the Medieval Climate Anomaly and the beginning of the Little Ice Age, then exacerbated by the robust trade routes stretching from China to Europe at the time. (Though they were beginning to crumble with the fall of the Mongol Empire.)
I actually just did a book review a few days ago on The Great Transition, which covers this exact period of history. Good read, if extremely dense.
All that being said, still a pretty big fan of your posts! (I especially liked the phosphorous post the other day.)