CASE NIGHTMARE GREEN is the demonological equivalent of an atomic chain reaction. Human minds equal plutonium nuclei. Put too many of them together in too small a place, and they begin to get a wee bit hot. Cross the threshold suddenly and emphatically and they get a lot hot. And the elder gods wake up, smell the buffet, and prepare to tuck in.

Our organization was formed as the British Empire's occult countermeasures organization during the struggle against Nazism, but it has continued to this day, serving a similar purpose: to protect the nation from an entire litany of lethal metanatural threats, culminating in the goal of surviving CASE NIGHTMARE GREEN. The UK's in a good position: a developed country, overwhelmingly urban (meaning its inhabitants are located in compact, defensible cities) with nearly neutral population size (no hot spots), and the world's most sophisticated surveillance systems. If you think the UK's been sliding into an Orwellian nightmare for the past decade, policed by cameras on every doorstep, you're right—but there is a reason for it: the MAGINOT BLUE STARS defense network and its SCORPION STARE basilisk cameras are fully deployed, ready to track and zap the first outbreaks. There are other, less obvious defensive measures. Our budget's been rising lately; ever wondered why there are so many police vans with cameras on the streets?

CASE NIGHTMARE GREEN is coming, and it's going to be perilous in the extreme. It's a bigger threat than global warming, peak oil, and the cold war rolled into one. We may not live to see the light at the other end of the tunnel, as we finally drift out from the fatal conjunction and the baleful stars close their eyes and reality returns to normal. Survival is far from assured—it may not even be likely. But one thing's for sure: we're going to give it our best shot.

THAT EVENING, AFTER THE PLUMBERS HAVE UPGRADED OUR defenses and Andy has finished picking our brains and left, I order in a curry—paying strict attention to the spy-hole this time when answering the doorbell—then retreat upstairs with Mo, a bottle of single malt, and a box of very expensive chocolates I've been hoarding against an evening like this. I'm dead tired, my face throbs around the butterfly sutures, and I feel unspeakably old. Mo . . . is better than she was earlier, for what it's worth.

"Here." I pass her the Booja-Booja box as I sit on the edge of the bed and unroll my socks.

"Oh, you shouldn't—did you set the alarm?"

"Yeah."

"You're sure?"

The rest of my clothes are piling up atop the socks: "Trust me, any burglar who tries their luck tonight is going to get the biggest shock of their life." Biggest, because afterwards they're going to run out of life in which to cap it. "Remember you need to deactivate it before you set foot on the stairs. Or open any windows."

"And if the house burns down . . ."