"Eu-bloody-reka!" Owen's strident voice burst suddenly from the medical bay. "Somebody bring me a beer. I've earned it."

Gwen, who was fanning her arm with a sheaf of reports, leaned over the medical bay railing. "What did you do?"

"I've cloned my birthmark and… actually, I don't want to explain this more than once. Get Jack down here, will you?"

Gwen returned to her desk to collect the bottle of tanning cream she'd been applying to her arm, then knocked at the door of Jack's office. "If you've finished conferring with UNIT, Owen's done something brilliant and wants to show off to everyone."

Ianto assembled a tray of coffee and biscuits before making his way to the medical bay, where everyone except Owen gratefully partook of the liquid energy. Ianto set Owen's mug a few feet away, safely out of range of the sterile equipment on the table. He thoughtfully placed a bottle of ale beside it, on the off chance that Owen had earned one.

"So what's the news?" Jack sipped from his mug as he scanned the array of test tubes and petri dishes.

"I've made a breakthrough," Owen announced, spinning in his swivel chair. "And I believe we can officially finger SoulMatch for the drone."

Jack's nose wrinkled in disgust. "I officially don't have any interest in fingering anyone involved with their operation. And that's me saying that," he added with a patented Harkness grin.

Owen rolled his eyes. "Yes, Jack, we recognize that your refusal to have sex with the enemy means that it's serious."

"So what did you do that merited a 'eureka'?" Gwen finished daubing the next coat of tanning lotion on her arm with a cotton swab and blew gently across it.

"To start, I took a sample from my own birthmark and cultured it in some artificial skin." Owen pointed to a tray of sealed containers. Through their clear lids Ianto could glimpse odd patches of cream-colored membrane, some spotted with dark shapes. "Once it was established—which didn't take long—I ran a battery of tests, including exposing it to the mystery substance Tosh isolated from the drone. And guess what it did?"

"The suspense is killing me." Jack took another sip of coffee and reached across to collect a biscuit from Ianto's tray.

"Two things, actually. First, compare the appearance of the original culture…" Owen pushed one container forward. It contained a flap of synthetic skin with a faint tan blob in the center. "…to the treated sample." He put another container beside it. The mark on this one was dark brown, with hard edges as though it had been stenciled. Ianto glanced down at his own birthmark, which had grown dark and crisp over the past few months.

Toshiko peered at the cultures, fascinated. "The powder intensified the birthmark? How is that possible?"

"I'm still working out the mechanics, but I think you'll catch on when you see this." Owen donned a pair of nitrile gloves and unscrewed the lid of the second sample. Picking up a tiny electric probe, he touched it to the artificial skin. Instantly, a branching pattern like a bolt of lightning crazed across the birthmark, leaving pale lines through the darker area of skin.

"A Lichtenburg figure!" Toshiko leaned closer. "Except… it's in negative. Don't they usually show up red on skin?"

"Yeah, they do. But wait for it." Owen withdrew the probe. The lightning pattern remained, stark against the birthmark. Then, as they watched, the edges of the lines began to fade. After a couple of minutes, the birthmark had restored itself.

Jack gave a low whistle. "Okay," he admitted, setting down his coffee, "that's interesting."

"But what does it mean?" Gwen asked. "How did it change the mark?"

"Whatever is in the powder—and Ianto's capsules—makes whatever is in the birthmark more receptive to electrical impulses," Owen explained. "The human body is already an electrical powerhouse, but the pigmented section is like its own tiny power grid. It reacts completely differently than other human tissues. And as you just saw, it can automatically restore itself when interrupted by electric current."

"So, not actually a birthmark, then?" Ianto asked.

"Nope. At least, not in the natural physiological sense. I mean, obviously people are born with them, but it's not just a melanin deposit."

"But if it isn't a birthmark, what is it?" Toshiko glanced between Owen and Jack. "Some kind of implant? A parasite?"

"Nanotech," Jack said suddenly, clicking his fingers. "It makes sense now—that drone was meant to disperse nanites. Get them into people's bodies. That's the reason for the aerial dispersal—the nanites can find their way into a body no matter how they come in contact with it."

"Nanites, as in the tiny robots?" Gwen frowned. "But I thought Tosh had already scanned the pollen for alien tech."

"I did," Toshiko confirmed. "I didn't find anything. There was no trace of metallic or synthetic elements in the powder. It was all completely organic."

"Which means it's probably nanobiotech," Jack said.

It was Toshiko's turn to frown. "Nanotech, I'm familiar with. But what's nanobiotech? And why didn't it show up in my scans?"

"Because it's smart. It mimics the body's own nervous tissue. I don't know that much about the mechanics of it; it was still in development in my time. Real cutting-edge medical tech. It's completely organic, designed to adapt to the body with minimal rejection. The big problem with synthetic nanotech was providing the bots with an energy source, but supposedly this stuff would piggyback off the body's natural processes, powered by body heat and the electricity from nerve impulses. Once it's installed in the body, bioscans would only pick it up as a slight increase in bioelectric activity—if they could detect it at all."

"But what's the point of giving people birthmarks made of tiny robots?" Gwen asked. "I mean, I could see infecting humanity if they were trying to take over the planet or something, but all SoulMatch has done for the past decade is play matchmaker to the world."

"And if these nanites are in the powder that's being dumped into the air, why aren't we all affected?" Toshiko asked. "Why is there an age limit on who has birthmarks?"

"I'm guessing the critical hardware installation has to be done before birth," Jack said. "Maybe it's something to do with prenatal development or tissue growth, I don't know. Or maybe the drone powder is just a firmware update. In any case, it's something that shouldn't be in this time and place, and it's clearly alien in origin, so we need to put a stop to it."

"How?" Owen asked. "Surgical removal? Because I think most of the population might not agree to that."

Jack shook his head. "These things aren't complex enough to think autonomously. They operate remotely, probably on a master signal. If someone's actively controlling the nanites, there should be a way to shut them off at the source. Ianto," Jack turned suddenly to him, "you've seen their operation. How much personal monitoring are they doing? Unique subjects?"

Ianto thought back to what he'd overheard in the lounge. "Dr. Peters said something about being able to locate a particular person, so I think they must have a way to track individuals geographically."

Gwen looked aghast. "What, like SatNav? You mean they're monitoring all of us via GPS?"

"The nanites don't have that strong a signal," Jack assured her. "It would take too much power. But if they're able to locate people…"

"That means they have the ability to triangulate," Toshiko concluded. "I'll bet each SoulMatch office is part of a greater wireless communication network."

Jack nodded. "And if we could hijack that signal, we could at least interfere with their operation. Maybe even order the nanites to self-destruct."

Gwen bit her lip. "Would that be safe? I mean, if you're right about the birthmarks, these things are embedded in the bodies of billions of people, including three of us! What happens if they go wrong?"

Owen was probing another of his samples. "Nothing, I think. The components we identified are all compatible with the human body. If they stop functioning as a unit and drift into other tissues, in theory, the body should just reabsorb them."

"And then what?"

Owen shrugged. "Eventually they're broken down, filtered like all other toxins in the bloodstream, and excreted out."

"Okay," Jack said. "So we find whatever system they're using, and we take it over. Shut it down if possible."

"Right," Ianto murmured. "Just pull the plug on a multi-billion-pound international company with a ten-year head start on infrastructure. Seems simple enough."

Owen shot him a dark look. "What I've always appreciated most about you, Ianto, is your shining optimism." He stripped his gloves and rolled his neck. "Now that I've made my astounding contribution to the world-saving effort for the day, where's my beer?"