Perhaps every fictional series should have a Christmas story - or a Jewish etc equivalent? I can cite three prominent examples:
in Conan Doyle's Sherlock Holmes series, "The Adventure of the Blue Carbuncle" (see here);
in Poul Anderson's History of Technic Civilization, "The Season of Forgiveness";
in Ian Fleming's James Bond series, On Her Majesty's Secret Service.
There are other Christmas stories but are they parts of series?
There are other series but do they have Christmas stories?
Now blog readers can tell me what I have missed.