This is an entertaining short story (and free download) in Charles Stross's Laundry
series. A civil servant in a secret British organization dedicated to keeping eldritch horrors at bay is the only one who can prevent the Bringer of Gifts from ending the world on Christmas Eve. It reminded me a lot of the Buffy episode "The Zeppo." Stross is in love with cleverness, so there are lots of geeky in-jokes, but I got them and found them amusing. I may go read his "Laundry" novels now.