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…”

“And if the house burns down, yes.” I shove the pillows up against the headboard. “We’re safe here, as safe as can be.” Which isn’t saying much if the bombshell Andy dropped turns out to be true, but I’m not about to remind her of that. I lean back. “A wee dram?”

“Don’t mind if I do. How about death by chocolate?”

“Sounds good to me.”

For a minute we’re silent; me filling two glasses, Mo working her way into the box of cocoa-dusted delights. Presently we exchange gifts. Outside, it’s raining: the rattle and slap of water on glass merges with the distant noise of wheels on wet road surfaces, but inside our insulated, centrally heated bubble of suburbia we’re isolated from the world.

“By the way, I haven’t said thank you, have I?” she asks.

“What for?”

“Picking up the pieces, bollocking Andy for me, being a dear, that sort of thing. Just existing, when you get down to it.”

“Um.” I put my glass down. “Thank you. For saving my life this afternoon-”

“-but if you hadn’t punched his legs out from under him he’d have shot me-”

“-he was going to shoot me first! Did you see where-”

We stop, looking at each other in mutual disbelief and incomprehension.

“How did we get here?” I ask her.

“I don’t know.” She frowns, then offers me the box of chocolates.

“Pick one.”

I pick something that looks like it came out of the wrong end of a hedgehog, except that it smells better. “Why?”

“Let’s see… that one’s unique in this collection, right? Let’s consider life as a box of chocolates. All of them are unique. Let each chocolate be a, a significant event. All we can say of any chocolate before we eat it is that it was selected from the slowly diminishing set of chocolates we have not already encountered. But one thing they’ve all got in common is-”

“Theobroma cacao,” I say, shoving it in my mouth and chewing. “Mmph.”

“Yes. Now, let Theobroma cacao stand for the defining characteristics of our reality. We don’t know precisely what the next chocolate will be, but we expect it to be brown and taste heavenly. But the previous chocolates we’ve eaten have narrowed the field of choice, and if, say, we’ve been picking the crunchy pralines selectively, we may find ourselves experiencing an unexpected run of soft centers-”

“I thought we were taking them at random?”

“No; we’re picking them-without a menu card-but we can choose them on the basis of their appearance, are you with me? We can choose our inputs but not the outputs that result from them. And we have a diminishing array of options-”

“What kind of chocolate did you pick in Amsterdam?” I ask.

She pulls a face. “Wormwood. Or maybe Amanita phalloides.” (The death cap mushroom, so called because the folks who name poisonous toadstools have no sense of humor: it’s shaped like a cap, and you die if you eat it.)

“Are you ready to talk about it?”

She takes a sip of Lagavulin. “Not yet.” Her lips twitch in the faintest ghostly echo of a smile-“But just knowing I can unload when I need to-” She shudders, then abruptly knocks back the contents of her glass in one.

“Do you believe Andy?” she asks, presently.

“I wish I didn’t have to.” I pause. “You mean, about the, the-”

“The acceleration.”

“Yeah, that.” I fall silent for a moment. “I’m not sure. I mean, he says it came out of Dr. Ford’s work in Research and Development, using analytical methods to observe bias in stochastic sequential observations at widely separated sites, and Mike Ford’s not the kind of man to make a mistake.” Sly and subtle, with a warped sense of humor-and a mind sharp enough to cut diamond, that’s our avuncular Dr. Ford. “I’d love to hear what Cantor’s deep-duration research team at St. Hilda’s made of it, but I suspect you’d have to go all the way to Mahogany Row to get permission to talk to them about current work-they’re sandboxed for a reason.” Mostly to protect everybody else’s sanity: it’s a team of no less than four DSS-grade sorcerers working on a single research project for more than thirty years. They’ve grown more than slightly weird along the way. Just talking to them, then thinking too hard about their answers can put you at risk of developing Krantzberg syndrome, the horrible encephalopathy that tends to afflict people who spend too much time thinking about symbolic magic. (The map is one with the territory; think too hard about the wrong theorems and you shouldn’t be surprised if extradimensional entities start chewing microscopic chunks out of your gray matter.)

“I want to see Ford’s raw data,” Mo says thoughtfully. “Someone ought to give it a good working-over, looking for artifacts.”

“Yeah.”

She puts her glass down and plants the box of chocolates on top of it. “If the acceleration is real, we’ve only got a few months left.”

And there’s the rub. What Ford has detected-so Andy told us-is an accelerating rip in the probabilistic ultrastructure of spacetime.