I read cozy and historical mysteries, a bit of Paranormal/UF, and to mix it up, I read science and gardening books on occasion.
A quick short story that doesn't seem to really need to be read before or after any of the books beyond book 2 or 3 (they are obviously married here). Not at all Christmassy, but entertaining, as Mary tells Holmes about one of her more colorful relatives and her first stroll down the less law-abiding side of life.
(I found it on Smashwords, but I believe it's available on Amazon as well.)