Jacob says, "These are all of Derek's phone calls."

He looks from the computer screen to Veronica. Her expression is hard to read; the half-healed cuts on her once-perfect face make her look like an extra in a zombie movie. Jacob supposes he still resembles an acne-scarred teenager himself. At least his goatee conceals the worst of the damage.

He wishes he'd cleaned up his apartment a little before she came over. It's a nice enough place, two bedrooms all to himself, but it isn't really ready for guests. His bedroom is strewn with scattered clothes and books, and the rest of the place is devoid of furniture except for his computer desk and a couple of chairs. The white walls are bare, the kitchen cabinets are empty, and most of his possessions are still piled in suitcases and toiletry bags. He doesn't even have bookcases yet: dozens of science-fiction novels and technical texts sit in stacks on the carpeted floor of his computer room.

Jacob looks back to his computer, and to the Google Map of Uganda on its screen, a map half-covered by little orange and red balloons that serve as place markers. Red outnumbers orange by a wide margin. Most are clustered in Kampala, but there are a fair number out west, near the Congo border, and a few orange balloons scattered in other places as well.

"Red is Derek," he explains, "orange is the other participant, if they're on Mango."

"Where did this come from?" She sounds more perplexed than impressed.

"Oh." Jacob realizes he has been remiss in providing context. "Derek had a Mango cell phone. Mango is a division of Telecom Uganda. I work for Telecom Uganda and have admin access to their databases. And the reason they hired me is there isn't much I don't know about mobile communications systems. This is what I've got so far. Would have been more, but I spent my first three days back basically fully zoned out."

Veronica nods with understanding.

Jacob switches briefly to a black window full of orderly rows and columns of text. "The records of every call Derek ever made or received, including," he points at columns on the screen, "the other number involved in that call, Derek's location, and if the other participant was also had a Mango phone, their location as well. I converted this data to XML and plugged it into a Google Map. Et voila."

"Location? You can actually track cell phones? I thought that was just in movies."

"No, you can, for real. What happens is, we record which base stations handled the call, and the signal strength they got from your phone. Base stations are the cells, the fixed antennas your phone talks to. We know their exact location. So if three or more were in range, we can triangulate a phone to a single patch of real estate."

"How close can you get?"

"Well, it varies." Jacob decides not to get into too much detail. "Depends on how many base stations and how far apart. Error margin is probably somewhere from forty metres in downtown Kampala to half a kilometre in rural areas. It's not quite like the movies, you can't actually track individuals, because the closer you can get, the more densely populated the real estate, they got lost in the crowd. But you can get a pretty good idea of their general vicinity."

"And you have names too? You know who he called?"

"No. Unfortunately. Mostly. If they're actual Mango subscribers, yes, but almost every phone in Uganda is prepaid, not subscription. But I bet if we look hard enough at this list we'll find some interesting stuff."

"This is why Derek brought you to Africa," she says slowly.

"Exactly. To track the call records of whoever he was interested in."

"You really think you can find out who set him up from this?"

"There's a lot more I can do than just this. But it's a good place to start. Retrace his steps, work out who he's been talking to." Jacob switches back to the Google Map. "Red is where Derek was during the call, orange indicates the other person's location, if it was a Mango-to-Mango call. I can't track people on other networks."

"So that red marker up at the Congo border means Derek was out there?"

He nods. "Yeah. Good example. Let's take a closer look at that."

He scrolls over and zooms in. One red and one orange balloon, both labelled with question marks, float over the Semiliki district, right up against the Congo border a good three hundred kilometers north of Bwindi. Jacob clicks on each marker and examines the call data that pops up on the side of the screen.

"He was there three weeks ago," he reports. "Or at least his phone was. And this orange one there, this other number, it's Mango too, he called it repeatedly over the last month."

"Prester said there was a smuggling ring," Veronica remembers. "From the Congo to Uganda. And Semiliki's right near the border."

"Exactly."

"What do the question marks mean?"

"Geographical uncertainty. If there's only two base stations in range of a phone, then you can only track it to one of two locations, where their circles of coverage meet. But Semiliki is way out there. Only one base station."

"So we can't tell where exactly he or the other phone was."

"Probably not. Unless - let me check." Jacob switches back to the black window full of text, and opens up an SSH connection to Telecom Uganda's master database server. His fingers rattle with machine-gun speed over his keyboard as he composes a moderately complex database query, calling up the exact details of all calls involving Derek made near Semiliki.

He runs the query. Telecom Uganda's servers ponder the question for a few seconds; then rows of numbers begin to scroll rapidly down across the screen. Jacob persuses them. After a moment he grunts with surprise. Both the handsets in question, Derek's and the other one, were used far enough away from Semiliki station that their signals regularly arrived twenty microseconds out of sync from their allotted timeslot. That's something. Radio waves move at the speed of light: three hundred thousand kilometres per second, aka six kilometres per twenty microseconds. There's no way to work out the handsets' direction from the station when they were used, but Jacob knows they were exactly six kilometers away.

He relays this information to Veronica, and adds, "Semiliki's a small town, more like a village, there's nothing else out there. And the base station's right in town. So what was Derek doing that far out?"

"Maybe that's the smugglers' hideout?" Veronica suggests tentatively. "Maybe Derek went out there, and that's how he found out too much?"

Jacob frowns. It sounds a little too neat. "Maybe. I don't know. It's not like a secret terrorist cell would have called up a white boy and invited him out to come look at their operation. Tell you what. Let's take a look at what's out there."

Jacob launches Google Earth. A new window opens up on his computer screen, and within it an image of the world as seen from orbit. He copies and pastes data from the other window, instructing the software to traverse the six-kilometre loop around the coordinates of the Semiliki base station. Veronica murmurs with surprise as the image zooms in towards the earth, as if the window was a camera on a falling satellite.

The virtual eye in the sky swoops downwards from orbit, towards Africa, into Uganda. They see roads, forests, clouds over the bristling Ruwenzori mountains south of Semiliki, the blue expanse of Lake Albert to the north, the gray grid of Fort Portal. The virtual camera levels off a few thousand feet above ground and begins to fly in a tight loop. Jacob smiles at Veronica's surprise.

"This is the six-kilometre radius around Semiliki base station," he explains. "What you're seeing are real recent satellite photos, stitched together automagically into a single landscape. Pretty cool, eh? It's like having your very own Pentagon war room, for free."

Hilly terrain scrolls past, and is interrupted by what looks like a wide red scar in the green earth, a blotchy discontinuity several square kilometers in size. The resolution is too vague to see details, but within the red smear, oblong green and gray shapes are arranged in vaguely geometric patterns that suggest human habitation.

"What's that?" she asks.

Jacob freezes and peers at the display. "Must be some kind of town. Weird. Deeply weird. It looks way bigger than Semiliki, but it's not on any of the maps. Let's do a quick web search on latitude and longitude and see what we get."

He launches a web browser.

"Fast connection," Veronica observes. "Mine's really slow."

"Yeah. There's no fiber link to east Africa yet, everything's through satellite, it's a pain in the ass, high latency. But this computer has a DSL connection to the hub, and I've given my personal data the highest priority on their satellite link. Making this literally the fastest Internet connection in Uganda."

He goes to Dogpile.com and types in the geographical coordinates of that mysterious settlement near Semiliki. Dogpile delegates the request to all of the world's major search engines, and assembles the collective results into a single list. The first entry is entitled UNHCR Semiliki.

"UNHCR?" Jacob asks, perplexed.

"I know that one." Veronica leans forward, interested. "United Nations High Commission for Refugees. It must be a refugee camp. Didn't Susan say the camp she worked at was in Semiliki?"

"Did she? But that's not Susan's number." Jacob doublechecks. "No. She's not on Mango. This is another phone. Someone else at that camp."

"Someone else." Veronica considers. "Maybe Susan knows who. Maybe Derek didn't invite her to Bwindi just because she's blonde and pretty. Maybe she was a lead."

"Huh." Jacob leans back instinctively to think, winces as the pressure causes the five whip wounds on his back to flare up, and hunches forward again. He closes his eyes and tries to arrange all the facts swimming in his mind, order them into some logical sequence. "OK. So Derek was investigating a smuggling ring and rumours they were connected to terrorists. He invites you and Susan to Bwindi because he wanted to make friends and sound you out, Susan because she worked at the camp, you because of Danton."

"Where else?" Veronica asks. "Where were his other calls? Where in Kampala?"

Jacob switches back to the map full of balloons, and zooms in on the Google street map of greater Kampala. There are markers almost everywhere in the city, both red and orange, but a few dense clusters stand out.

"This is here," Jacob says, indicating a little cluster on the east side of the city. "Calls to my phone. This is Derek's apartment, by the Sheraton." A dense clump of red near the center of town. "And here's his office." A thick cloud of red and orange to the north. "Those orange markers in his office, that other number, that must be Prester."

"What about this?" Veronica asks, pointing at a pile of orange markers a little south of downtown, between the Sheraton and the taxi park.

"No idea. They're all the same number. Not Prester, not the Semiliki number, someone else." He checks back against the raw data. "He started calling that number three months ago, and he's been calling them ever since, a couple times a week. What do you think that means?"

"I don't know. None of this makes any sense to me." She looks at him. "Why are you showing me all this?"

He hesitates. "I thought you'd be interested."

"I am, I guess. But why not take it to Prester or the US Embassy or something? Or did you already?"

"No. We can't do that."

She blinks. "Why not?"

"Think about it. Derek was set up by someone he was working for. Or with. I take this to the wrong person, they find out what I can do, they'll cover their trail and I'll just be getting myself into more trouble. I go to the Canadian or British embassy, they'll just pass the word on to the USA. The real reason I'm showing you is because you're the only person I know I can trust."

Veronica shakes her head. "You're being paranoid. I'm sure Prester or Strick –"

"You know what Derek was doing in the last couple months before we got grabbed? Investigating Prester."

Veronica stares at him.

"Yeah. Some big boss in the CIA, I don't know who, Derek never told me details, found out there was something rotten in the state of Uganda and sent Derek to investigate. When I got here Derek had me track Prester's phone calls. And in the last week before we went to Bwindi, you know what? He had me tracking Strick's calls too."

"But – no. Not Prester." Veronica thinks of what he said to them in Goma, in the lava field. "He told us what was happening. He was trying to help us."

"Or he was telling us what he wanted us to believe. Plus a few things we would have figured out or found out by ourselves anyways, but we heard them from him first, so it looks like he's a good guy. And while he's at it he just so happens to warn us to stop poking around and get the hell out of Africa for our own good. Just like Strick. They both wanted us gone."

"Maybe because they want us safe," Veronica points out.

"Maybe not."

"They don't even like each other."

"They're intelligence professionals," Jacob says. "They know how to seem like something they're not."

"You sound totally paranoid."

"Only the paranoid survive."

"Come on," she objects. "This is crazy. I mean, even if you're right, like you say, all you're doing is just getting yourself into more trouble. You want to know what I think? I think you should stop playing Sherlock Homes and go home."

"He was my best friend," Jacob says sharply. "Someone set him up. And us too. Someone murdered him, someone he was working with. I'm not just walking away."

A long moment of silence passes.

"You seriously think Prester and Strick might be working with Al-Qaeda," Veronica says, putting as much incredulity into her voice as she can.

" I doubt whoever it is knew their smuggler friends were in bed with Al-Qaeda until after we were taken. And now they'll be extra desperate to cover their tracks. Maybe it's just one of them. Maybe neither and Prester was telling the truth, it's somebody at the embassy." Jacob pauses. "Derek thought your ex-husband was involved. There might be something there."

"Like what?"

"I don't know," he admits.

"Did Derek tell you about Danton?"

"No. All he told me was what phone numbers he wanted information for. He wouldn't give me details, he said it wasn't safe." Jacob spits out the last few words angrily. "If he'd told me, maybe I would have seen it coming. Or at least now I'd know what he knew."

"Or whoever set him up would have found out you knew too much too," Veronica points out. "And you would have been number two on the chopping block."

Jacob pauses. She's right. Derek's secrecy may have kept him alive.

"So what are you planning to do?" Veronica asks.

"What we need is evidence," he says. Veronica raises her eyebrows skeptically at the we. "Once we've got hard actual evidence of who it was, then we can go to the embassy, take it straight to the ambassador, make it public."

"You really think you'll get hard evidence out of this?" She points to the computer screen. "Tracking a bunch of phone calls?"

"I think we're finding lots of stuff out already."

"Stuff that doesn't make any sense."

"It will eventually," he says confidently. "We just have to be methodical. Gather data, make a hypothesis, test it against the evidence, repeat until understanding is attained. The scientific method. It's cracked problems a lot harder than this one."

Veronica shakes her head, unconvinced. "Jacob, you want to know what I think, you should just go home. Maybe both of us should."

Jacob pauses. He can't help but wonder if she's right. Living in danger, investigating mysterious conspiracies – that was Derek's line of work, not his, he's just a techie, of unusual ability to be sure, but he's no swashbuckling superspy. It's true he came to Uganda to help Derek, and it was exciting knowing he was really working for the CIA, it felt like a big, wonderful adventure, like being in a movie, a supporting character to Derek's starring role. But Jacob never dreamed he might find himself in real danger. Until Bwindi. Until it turned into a horror movie.

The safe thing to do is to stop investigating and hope the authorities can find Derek's killer. But he can't turn his back on the murder of his best friend. It wouldn't be right. It wouldn't be honourable. Jacob has always thought of himself as someone who would do the right thing, in extremis. He supposes most people do. But most people never actually have to find out. He does, and right now. His whole life, quiet and ordinary until now, has in a way just been a prelude to this. What he chooses to do now is the measure of who he is. And if he fails, if he gives up and goes home, he will feel that shadow hanging over him for the rest of his life. He has to at least try.

Jacob tries to think of some way to convince Veronica to stay and help. He can trust her. He doesn't want to have to deal with this alone. And if Derek was right, Veronica's ex-husband is somehow involved in all this. But no brilliant insight or debating tactic that might convince her comes to mind.

Veronica's gaze drifts back to Jacob's computer, to the Google Map full of markers that indicate where Derek placed and received his phone calls.

"Wait a minute," she says, sitting up straight, suddenly alarmed.

He blinks. "What?"

"That terrorist phone Susan picked up. By the satellite dish. Remember what Prester said? It had two hundred phone numbers for Westerners in Congo and west Uganda."

Jacob nods. "And?"

"So they could track those phones like you tracked Derek's calls, right?

He hesitates. "If they had access to the databases, yes. But like I said, the higher the geographical precision, the denser the population. You can't locate specific individuals, they inevitably get lost in the crowd."

"Not in Africa. Not if they're white and the rest of the crowd is black."

Jacob opens his mouth but says nothing at first. She's right. The industry truism that cell phones can't be use to track down their owners is in this case false. White people stand out in Africa, especially rural Africa, like pink paint on black canvas.

"You think they're planning to –" He shakes his head. The idea is too huge to accept all at once. "You think Al-Qaeda are going to try and hunt down all those people. Using their cell phones. That's, no, that's crazy. How would they get access to the databases?" Jacob answers the question himself. "Oh, no. Holy shit. Through their partner in the CIA."

They stare at one another.

"Derek thought whoever was he investigating had an in at a phone company," Jacob says. "The first thing he did was have me make sure Mango was safe for him to use, check that nobody else was tracking his calls."

"We have to tell someone," Veronica says. She looks shaken.

"Don't panic. Not yet anyways. It's just a theory. And I'm sure the powers that be have thought of it too by now." Though Jacob is not at all sure of this. "We don't have any evidence. And I still can't believe a CIA agent would work with Al-Qaeda."

"They would if they were being blackmailed," Veronica suggests. "Help track these phones or we reveal how you were the smuggler who set up the kidnapping and murder of your own agent plus two other Americans."

Jacob nods slowly.

"Two hundred people. A lot of them, like Peace Corps types, out in rural areas, totally on their own. My God, they'll kill them. Or take them hostage first, like they took us. We have to do something. We have to go to someone."

He shakes his head. "With what? We have zero evidence. Just theory and supposition. And go to who? If we pick the wrong person, if they find out we're chasing their trail and I was working with Derek all along…" He hesitates. "They might come after us. They probably would. Whoever it is, they're not fucking around, we know that already."

Veronica swallows. "So what do we do?"

Jacob looks back at the computer screen and considers. "There's still too many unknowns. We might just be jumping at shadows here. I say we try to find out more before we do anything."

This time Veronica lets the we pass unchallenged. "How?"

"Go back to plan A. Retrace Derek's steps, find out what he knew." Jacob points to the cluster of orange markers on the map near Kampala's taxi park. "I'd like to know who this is, for starters. Must be a friend of Derek's, they talked a couple times a week, every week. Frequently immediately before or after calling the number in Semiliki. What do you say we go pay them a visit?"

Veronica looks at him uneasily.

"Come on," Jacob says. "Downtown Kampala, broad daylight, a friend of Derek's. It's not dangerous in the slightest. I promise."