"Weapons?" Ryder kicked off.

Derek laughed, then said, "Yes, let's not start with introductions and niceties."

"That's my job," Brian said, with a soft Welsh lilt in his voice. "Just to clarify for those unaware of our situation here, I'll give my usual spiel.

"Welcome to Anafon Field Study Centre. One of four run by the Biological Studies Department of London University. My name is Brian Wagstaff. I am the manager of this centre. My wife, Bronwyn, has shouted at all of you already. She does the jobs I don't know how to do, along with the catering. Teresa is a bio lecturer and one of the main reasons for our existence. Ryder is her bit of fluff-sorry, I only do jokes in bad taste. As far as I know, Ryder is an expert on making docs on space-related stuff and Derek is his boss. A dab hand at communications and computers, I hear, so I hope you can take charge of that lot, Derek? Good. Our beautiful French lass is Laurette who is in charge of the techies at the uni, including our Kraut, no offence meant, friend, Gustav. Will that do?"

"Have we any firearms?" Ryder said. "Or are we going to have a role-playing game now?"

Gustav looked worried and speaking in a Bavarian accent asked, "Why would it be necessary to have guns, Ryder?"

Laurette turned on him. "How can you be so stupid? We are here to keep those morons away from us. They'll be coming when they run out of food."

"Yes," Ryder said. "And to shoot the rabbits, sheep, and ponies."

Audible gasps escaped from his listeners.

"We have to assume all mammals may carry the ARIA virus," Ryder said. "It's them or us, which do you want?"

Ryder saw the shock on their faces.

Brian said, "I agree with your suggestions, Ryder, that we should keep this place as inconspicuous as possible. You know, blackout at night, trips to town as few as possible-"

"None at all," interrupted Ryder. "It just takes one of us to catch it in a shop and we've all got it."

Teresa said, "Is there anything we absolutely would need to go into Conwy for? Isn't the storeroom here fully stocked?"

Bronwyn sat upright to assert her quartermaster status in her strong Welsh accent. "It depends on what you call needs. We have enough basic foods to sustain seven people for at least a year, maybe more. You know: flour, pulses, dried foods of all descriptions, three walk-in freezers chocka; then we have a storeroom laden with tinned and bottled preserves and so on. But fresh fruit and vegetables, fresh meat, fish and other short-life foods?"

"We'll have to get along without fresh produce except what we can glean from the valley here," Ryder said.

Brian laughed. "The fish in the lake are not the tasty sort, the sheep are there until you shoot them, but some farmer might decide to investigate if his flock started disappearing. Anyone for wild horsemeat? There's plenty of frozen meat and vegetarian alternatives. In fact, the veggie proteins such as the soya, Quorn, and tofu proteins will last years."

"Brian," asked Derek. "Is this place usually as well stocked as a ship on a world cruise?"

"We often stock up when expecting field trips. This valley is awash with brightly coloured tents when the first-year biology trips descend on us, aren't they, Teresa? Then we usually get summer bookings from London schools-"

"Hey, there aren't any booked in for the foreseeable future, are there?" Ryder asked.

"No. There were a few pencilled in and we cancelled. What I'm saying is that we are equipped for mass catering, and because of our remoteness, storage was built in as a priority. But as for your persistent firearm question, the answer is no."

"Thank God," Gustav said.

"We'll need to acquire some," Ryder said.

"How? We don't have a gun licence."

"Actually, we do," Brian said. "Again, because of our isolation, the university rifle club have weekend practice shoots here. They make a range out in the valley. Come to think of it, there might be a rifle in their locked store. I don't have a key for it."

"Good, let's see," Ryder said. "Otherwise a couple of us will go on a raid."

"Mes amis, I'm not happy with lethal weapons," Laurette said, her short black hair glistened from being recently washed.

"We have to be realistic. All the local farmers will have shotguns and their sons will have air rifles, crossbows, stun-dart projectiles, and more diabolical weapons. I wouldn't want to go against them with just a butterfly net. Let's have a look at the rifle club's lockup, Brian."

Brian led the entire group through empty dormitories with their own kitchenettes until, to Ryder's surprise, sunlight hit him as they marched across a small quadrangle with a pond, seats, and slate-floor patio. Into the next building they passed a couple of lecture rooms and labs until they reached the outside again. Embedded in the mountainside, a small building barred their entry with a hefty padlock. Brian held up a crowbar and grinned at his audience.

"No telling, mind."

"Tell that to the cameras," Bronwyn said, reminding everyone of the security cameras dotted around.

"As if anyone's watching," muttered Brian as he levered off the padlock. The small store within wouldn't allow in seven but Brian soon re-emerged. "Three rifles and two competition handguns. Night scopes and plenty of ammo."

"I thought possessing handguns was illegal," Derek said. "Not that I'm complaining."

His query triggered a blank look from Brian, who asked, "Should we leave them here with a new padlock?"

"No," Ryder said. "Anyone could go over the roof and crowbar in like Brian just did. And if attacked, we'd be foolish not to be able to get at them quickly. We'll hide them in the kitchen and lounge. Let's get back, we still have other security issues to sort out."

AFTER A COFFEE BREAK, they assembled in the refectory over a large-scale map of the valley. It showed the lane leading the handful of miles to the nearby coastal hamlet and Aber Falls, a waterfall, which in happier days attracted weekend ramblers.

Brian pointed at a couple of hillside bluffs jutting into the lane. "A gate here would make it difficult for intruders to get their vehicles to us. Mountain on one side and a steep, boggy slope to the stream on the other. We have enough timber and wire fencing for the job. I need a hand though."

Ryder watched a spider crawl up the wall. "I'm sure Gustav will help, and me too. But, Brian, do we have enough fencing for a perimeter fence?"

"Not to surround the centre, say, on the ridge a mile away in three directions. I'd say it was unnecessary. No one is stupid enough to risk breaking their necks coming down the near-vertical mountainside to the centre. We rarely get any visitors, especially from the old Roman road on the eastern ridge."

Gustav chipped in, "I've walked up there, there is a track all the way to Llanfairfechan but, as Brian says, remote. We could put a couple of hundred metres or so of fencing where people might wander down here, just to put them off and an official no-trespassing notice."

"Hey," Derek said. "Don't put 'No Trespass,' they'll come over in droves."

"Yes, I would," Laurette said, to laughter. "A notice saying 'Minefield' would annoy me but keep me off."

"But unbelievable," Brian said. "How about 'Active Firing Range?'"

"I'll rig up some cameras to keep an eye on the lane and the ridges," Derek said. "I'll fit them with movement sensors."

"Don't forget to tell the sheep then," Bronwyn said, making Derek scratch his head to look for an amended plan.

Ryder looked up from his notes. "What happens if someone gets through while we are asleep?"

Derek huffed up. "By the time I set up our alarm sensors and cameras, no one will reach here without us knowing about it."

Ryder noted the spider disappearing into a crack. "I'm sure, but then what? Suppose in a month or so, when we can be pretty sure ARIA will be everywhere, a villager wanders over the hill looking for food? We need to shoot them, don't we?"

Derek banged a fist on the table. "We have to shoot them. For our own survival. If ARIA continues in a person so that they end up with no memory at all-no speech, no knowledge of how to look after themselves, they'll die anyway."

Brian, fidgeting, said, "That's a bit drastic. Not just killing intruders but because they're losing memory. They won't forget to eat."

"Brian," said Teresa, "as we get older, gain intellect and experience, instinctive behaviour is subsumed. Some Alzheimer's patients forget to eat and drink in advanced stages when factors adding to their confusion kick in. I've been struggling to postulate how ARIA might affect someone if it continued to rob them of memory backwards until they were born. It is incredible. Imagine no speech. I expect for a while some cleverer people might cope somehow."

"Not really," butted in Laurette. "They merely employ clever strategies; postpone the worst effects until they forget how to read."

"Grim," said Ryder. "We can't take the chance of an ARIA-infected person reaching us. I'm afraid we'd have to kill them. It's drastic but necessary."

"Afraid so," Derek said. "I don't want to kill anybody, but if it's them or us..."

Ryder knew there was no compromise that made sense. But it might help the group come to terms with the awful decision if they painted it with a veneer of democracy. "We'll put it to a vote, agreed?"

Everyone nodded so Ryder said, "Right, raise your hand if you think we need to shoot to kill intruders."

Long faces looked at each other, each knowing the turmoil and anguish that comes with making life-and-death decisions. Derek put his hand up, followed by Teresa and Laurette. Ryder knew that Brian and Bronwyn had friends and relatives in the locality and would have great difficulties with this decision. They remained holding each other's hands.

Teresa had told Ryder that Gustav would squirm at the thought of any kind of violent action against people, no matter how justified. Gustav stared at his hands, clasped between his knees.

"Bugger," said Ryder, with the casting vote. "Let it be so then, though Captain Picard I'm not."

Some rose to get on with their jobs.

"Hang on," Ryder said.

"Yes, Captain?" said Brian, though his face didn't show humour.

"We have another decision and action plan to implement."

Brian and Bronwyn groaned but sat to participate again; their comfortable lives changed.

"Just suppose one of us makes an inadvertent contact with an outside person. Should we kill each other?"

They sat in a stupor. They hadn't thought it through like Ryder. His job had not the academic depth of Teresa or the technical skill of Gustav and Laurette. What he had, besides the skills of strict target setting and documentary-making, was the ability of spotting one component that could spell a million-dollar loss with a scrapped programme.

"I suppose so," said Laurette, the first to recover and developing a reputation as the one who'd pull the trigger first.

"There is another way," said Bronwyn. "Solomon."

"Did you have to tell them?" Brian said.

"That's his daft name for a mine not far from here. Tell them, Brian, you've been in it plenty of times."

"Eh? How do you know?"

"See, Boyo. You think I don't know where you slope off to with your pipe and bottles."

"Well, there is an old adit mine, they used to get copper and lead, fluorspar-"

"Never mind the geology lesson," Bronwyn said.

"Brian," said Ryder with renewed light in his eyes. "Could Solomon's mine-and I like the name-be an isolation habitation? Is that what you were thinking, Bronwyn?"

"Exactly. If one of us became contaminated, or thought we were, we could radio in and say we were staying in the mine until we knew we were all right."

"Excellent," said Teresa. Ryder looked at her, aware that she knew they were putting off a decision about what to do if the one in isolation had ARIA.

"Also," said Derek, "it could be used as a fall-back position in the event some blighters broke into our centre here while we were out and about."

They agreed to make a start after lunch. Derek loaded a rucksack with electronics and the other three men prioritised the securing of the one existing gate and construction of a second. Teresa and Laurette looked for any news on the web before setting off on a reconnaissance over familiar territory as biologists but now looking at the landscape as an assailant might.

Saturday 25 April 2015, evening:.

Anafon valley.

RYDER SAT IN A DECKCHAIR next to Derek, on a patch of gravel outside the centre. "To think we could have been living here in peace for years instead of up to our noses in pollution with our ears full of traffic noise in London." Long shadows of rugged mountains crept up and over them, but the relaxed men faced the golden-sunlit slopes opposite. A few cumulus clouds changed shape as if they tried to emulate the sheep below seeking greener grass.

"The novelty would have worn off, Ryder, and you'd be gasping for the sight of a London bus. I must say, the clean air and serene landscape helps to take the edge off this amnesia infection. How long do you think it'll last?"

"I'm no expert, I don't suppose anyone is, except maybe some alien watching us right now." They both looked up. The sky darkened but was too light for any stars to show, although Venus just peeped over the mountain to the east. "I suppose we hope this ARIA behaves like other viruses that lose their potency. Several months, with luck, and we can sneak back out there."

"And what will we find, Ryder? Will there be any jobs to go to? How much memory is lost per week?"

"My sister Karen guestimated it at around a year lost per week. She was hoping to verify it with some neurological studies in Houston before she was infected. Supposed to be sending us a communication tonight. In fact, I ought to set it up if Teresa hasn't already."

"Yes, she told me. I've put an icon on the screen for her; just click and play."

RYDER AND DEREK GRABBED A COFFEE and found Teresa in the computer lab, trying to raise Karen. The satellite link showed Karen's home with other images of her lab and another of Julia's home, the technician who'd promised to send them results of a blood test. Polished wooden benches housed banks of computers. The lab was built to accommodate a fieldwork class and most of the computers had connections to laboratory equipment. Piles of redundant student files mounded on benches in-between upside stools. A few screens flickered as Gustav worked alongside Teresa.

"Just a minute, Ryder," said Derek. "You said you linked up last Sunday. They've probably lost all memory for the last year."

"Possibly," Teresa agreed, "but they both had the advantage of anticipating it. They'd set up their electronic diaries, both in their personal web pages and synchronised with their NoteComs. Hopefully, they'll keep track and recall re-learnt stuff. We set up this communication to automatically remind them."

The connection burst into life, giving images of labs and a study. Within moments, Julia's face appeared on screen. Her red hair in disarray, her cheeks showed splotchy mascara decorating her red eyes.

"Julia, are you okay?" called Teresa into the mike, but Julia didn't appear to react as she fiddled with the keyboard.

"Maybe she's too upset to speak," Ryder said.

"No," said Derek. "This is a recording; she isn't live, so to speak."

"How can you tell?" Teresa said.

"Data on the task bar." He pointed at a movie symbol. "Just a sec, ah, voice input."

"...awful. I don't know where Karen is. My diary says we met up a couple of days ago when she collected the blood test results on the ARIA patients. She doesn't respond to her phone or e-mail. She might have gone with some others out to the Schenectady lab complex. They specialised in Alzheimer's research there. I have travel plans too. Sorry this is a recording but at least it allows you to know."

"Know what? Dammit," Ryder said.

"Listen, you idiot," Teresa said, batting him with a free hand.

"... inconclusive I'm afraid. We took blood samples from people definitely infected and looked for the same sort of indicators for Alzheimer's. These are variants of the P97 molecules and amyloid precursor protein. Slightly higher than in non-Alzheimer's patients. We used the electron microscope and found the usual assorted pathogens but the image of one I'm sending you with a package of data is a spiked sphere about 30 nanometres across. Looks like an adenovirus, but who knows? Teresa and Ryder, there are so many human viral pathogens to be found in saliva that haven't been identified, so it's damn hard trying to find one or a group of alien ones. There's nothing showing fluorescent green anyway. The one we suspect looks similar to one of the common cold adenovirus pathogens, so maybe that's why it spreads so easily-saliva of those infected is full of them and so would the air they breathe out. There is hope, then, since some people are immune to the common cold, so maybe they're immune to ARIA-I gather from a medic web page that's what it's called. I wish I was immune. Like Alzheimer's, it's probably slower in people who had high intake of vitamin E and ginkgo biloba. We should all be eating vitamin sandwiches.