The amazon.com product description:
Introduced to readers in the novels The Atrocity Archive and The Jennifer Morgue, the Laundry is a secret British government agency charged with preventing dark interdimensional entities from destroying the human race. Now, in "Overtime," the Laundry is on a skeleton staff for Christmas — leaving one bureaucrat to be all that stands between the world and annihilation by the Thing That Comes Down Chimneys. Written especially for Tor.com’s holiday season, Charles Stross’s novelette is a finalist for the 2010 Hugo Award.I've never read anything by Charles Stross before, but looking at the blurbs on the backs of his other books, I'd thought they looked interesting. So, when I got a chance to download this one, I didn't think twice (I don't think I even read the blurb).
It was only when I started reading the story and going "what?" that I realized that it was part of an established universe. Overtime is a Christmas themed story, and a funny one, given the way the author plays with all of the Christmas traditions we take for granted. The story also made me curious about the books set in this world. I may well have to check them out further. Not to mention the other books Charles Stross has written.
Being a short story, I'm not sure what else I can say without spoiling the story. However, I will note that it had me laughing out loud on the transit system while reading it, and the poetry is hilarious. Doesn't everyone have to play with that old chestnut "The Night Before Christmas" at least once?