RTW: Elevator Tales

Wednesdays are 'blog carnival' days over at YA Highway, where readers respond to questions posted by the YA Highway team. Today's question is:

You're re-reading one of your favs when someone asks the dreaded question: "What's that book about?" Give us your best off-the-cuff blurb of any book, any genre, and have your readers try to guess the title in the comments!
This is a great challenge as I often find I have trouble explaining things. (Also I find it weird when people talk to me on the lift, as if we're on the set of some sort of late-nineties romantic comedy and the old lady with the crazy hair, the tuna-fish smell and the shopping bags is about to tell me something profound and life-changing that twenty years later I'll be telling to my own kids when I tell them the story of my whirlwind romance with their father.) I'm the sort of person who, when asked to define a word, tells you to go and get a dictionary so that either a) I cover my own ignorance and shame at not knowing the answer, or b) I can cloak my own incompetence in a display of intellectual superiority.

So anyway, here goes:

"Okay. Um. So it's the story of Armageddon, right, but there's this angel and this demon who are both trying to stop Armageddon from happening for different reasons, but they unwittingly lose the Antichrist and he grows up as a normal little English boy. And it's all framed by the prophecies of this sixteenth-century witch who predicted the whole thing happening. And her great-great-great-something granddaughter is also trying to stop it happening with the help of a twentieth-century witchfinder. It's absolutely hilarious."

Any guesses? ;)