It's the beeping that alerts them first, unexpected as it is. Martha's leaning over Gwen for some lemon chicken; she drops it on Gwen's hand, and picks it up with a smile (half apologetic, half something else), tracing a finger across Gwen's skin to remove the sauce.

"Sorry," she says, and Gwen would say something in response, but then the beeping starts again. Leaving her lunch on the table, she stands, follows Jack over to her desk.

"What is it?" Martha asks, and she's close; Gwen turns her head, meeting Martha's eyes for a second before turning back to the alien device.

"I don't know," she says; Jack's already picking it up, carefully. "I was trying to get it to work earlier -"

"It's a tracker," Jack says, and a wave of recognition hits Gwen. She'd seen it listed, before, on the computer - Tosh's computer, still, and she thinks it probably always will be - just one more thing lying dormant with nobody left to use it.

Jack starts pushing buttons, until the beeping stops. Images flash on the small screen, something like a map; he smiles, and Gwen knows what's coming, waits for him to give the order.

"Change of plans. Lunch will have to wait."

-

Jack drives a little faster than is strictly necessary - he's eager to get out of the hub, Gwen thinks; they all are, since Tosh and Owen - while Ianto reads carefully off the device. In the backseat, Gwen's gaze falls on Martha, watching her reaction; she's calmer than Gwen expected, much calmer than she had been on her first day, her eyes dark with an anticipation Gwen recognises. (One she feels, even now, and she knows Martha's probably seen more than she has.)

Martha turns her head, her gaze locking with Gwen's, and Gwen could say that she reaches for her, her hand resting lightly across Martha's thumb, in reassurance; that the spark of electricity she feels is excitement for the mission. Martha smiles, and before she has to say anything, the SUV stops.

The street is empty, warehouses lining one side, semi-abandoned buildings on the other. No sign of what brought them here, and no obvious clues about what to do next.

"Gwen," Jack says, and she's already scanning the area; turns to him, waiting. "You and Martha check out some of those warehouses. Ianto and I will take the other side."

She nods, moving quickly, Martha beside her. She runs a hand along the gun at her hip, and sees Martha glance over at the movement. She had refused one, when Jack offered, and he'd nodded like he understood; Gwen's waiting, already, for her to change her mind.

The first warehouse is locked, predictably enough. Gwen almost strains her shoulder on the second, and Martha reaches out in sympathy; on the third, she braces herself, and almost jumps back when the door rolls upwards with a bang.

It's dark inside, bigger then she expected, but the light coming in from the street is enough to see by. Gwen has to blink a few times, let her eyes adjust; beside her, Martha sucks in a breath, and Gwen follows her gaze.

It looks like a table, some makeshift gurney she'd expect to see in a morgue; wires (restraints) are strapped to the side, and she doesn't even pretend to know what's in the tubes lining the wall, except that there's a reason the device led them here, and Gwen's pretty sure they just found it.

"What is all this?" Martha asks, softly, and Gwen shakes her head; she's just about to reach out, take her arm (they should get out of here, now, call Jack) when something moves in the doorway, and before Gwen can react, she's falling backwards, her head colliding with something sharp as she goes down.

She doesn't black out, though it's difficult to tell, at first; it's darker down here, the floor hard beneath her, a shape on front of her blocking the light.

"Gwen," she hears, and it's Martha; blinks, slowly, winces at the pain in her head. "Are you all right?"

Martha's kneeling down, her face close to Gwen's, one arm braced on either side of her as she leans in closer. Gwen tries to nod, cringes, and Martha's telling her not to move, stay still, I need to check if you're all right. Her eyes drift shut, sleep pulling at her, and it's only Martha's voice that keeps her grounded, opens her eyes and sits up, finally.

"Thank God," Martha says, and a second later she stands, helping Gwen up. "I thought I was going to have to kiss you."

They stay looking at each other like that for a moment before Gwen can feel her head start to clear, remembering why they're here, what just happened.

"What was that?" she asks, though she thinks she knows; Martha's eyes lock with hers, and she nods.

"Looked human to me," Martha says, as if she's asking for confirmation. Her hand brushes lightly against Gwen's as they move, slowly, back into the street. "Pretty fast for a human, though."

"And strong," Gwen says, feeling the back of her head. She'll have a bump there, later. A part of her feels as if she got off easily.

"Whatever it was," Martha says, and Gwen lets out a sigh at that - human or not, it wasn't just human - "it's gone, now."

And Gwen, she knows, should just leave it at that, nod and smile, but she's never been very good at forgetting. Besides, there's a sewer grating nearby, and she's been doing this long enough to think that a day at Torchwood probably isn't complete without a trip to the sewers.

Martha follows her gaze, shakes her head almost imperceptibly. "No," she says, but it doesn't sound like a denial. "We are not going down there."

But she follows Gwen, anyway, takes her hand as they land on the damp concrete underground. Now that she's here, Gwen knows that they should have found Jack first, should have told someone where they're going, thought about it for a minute before they rushed off in pursuit. Only they're here, now, and whatever it is they're following already has a decent lead. So she sets off, trying to move as quickly as she can without making too much noise; the creature - person - is probably long gone, but if it isn't, she'd rather not announce their presence. Her hand falls from Martha's, almost reluctantly; they're here on a mission, but Martha's still close, her presence comforting in the dank tunnels.

Which is a good thing for her, if not for Martha, when she stumbles; she falls, pitching forward as she scrambles for purchase, taking Martha down with her. Once her breathing returns to normal, she looks down, Martha pinned beneath her, and almost smiles; she'd make some sort of quip, now, she thinks (already thinking about how she'll need to shower, how her jeans are probably a lost cause), except Martha's looking beyond her, and Gwen rolls off, glances behind her shoulder.

She's glad she's not smiling when her gaze falls on the dead girl lying beside them.

-

"It's not contagious," Martha says, and Gwen can't help her sigh of relief. It's not a surprise, not really; if the girl had been contagious, chances are one of them would have caught it by now, and it's not like there's really anything they could have done about it.

"What is it?" Jack asks, and Martha sort of shrugs.

"I'm not quite sure. I could do more tests, but right now it looks like some sort of chemical agent."

"Alien?"

"I don't know. It doesn't look like it, but the original DNA's been altered. It might be."

"It fits with what we saw in the warehouse," Gwen says, and Martha turns to look at her.

"What else did you see?" Jack asks, and Gwen tries to think back.

"A table. Operating table, maybe, or just storage. Some chemicals."

Jack nods, exchanging a look with Ianto, who steps forward.

"One of the buildings we found," he says, like he's already got it figured out. "Looked like some sort of abandoned laboratory."

"Maybe not so abandoned," Jack says, and he sets his shoulders in resolve. "We're going to have to go back there, anyway. Check out the rest of those warehouses. I'm guessing our girl here isn't the only one they've been using for their experiments. While Ianto and I are doing that, Gwen, I want you and Martha to see if you can get into that lab."

"Got it," she says, and with a glance at Martha, prepares to move out.

-

Gwen shares a last look with Jack before she and Martha set out across the street. He and Ianto are already heading towards the first of the warehouses, prepared to force entry, this time, and Gwen's hoping she won't have to do the same with the lab.

As it turns out, she doesn't. The door is locked, but it isn't hard to push open, once she puts her weight behind it; Martha looks at her, eyebrows raised, and Gwen nods as she steps inside.

The lab isn't exactly what she expected; mostly empty, though it looks like it was cleared out in a hurry, a few stray notes strewn about on the floor and a small bank of computers against the far wall. There's another door in the back, and Gwen glances at it; wordlessly, Martha begins to move towards it, and Gwen reaches out to touch her arm, be careful.

The computers are off, unplugged, and it takes Gwen a minute to power them up. She says a small prayer that whatever's on them isn't encrypted - that was Tosh's domain, and it isn't times like this Gwen misses Tosh most, but it's times like this she feels it; like something's missing, still, a phantom limb, a friend that she valued more than she realised, back when it would have done her some good.

The computer screen flashes, and Gwen begins searching through files, looking for anything that might tell them what they're dealing with. If there are more people - or bodies, and Gwen isn't sure which would be worse - in those warehouses like Jack suspects, they're going to need something, she's going to need something, and the thought keeps her going through pages of empty or deleted files even after she's tempted to give up.

She doesn't hear Martha come up behind her, but she notices when Martha leans over, her hair brushing Gwen's shoulder. She can almost feel Martha's breath on her cheek, resists the urge to turn her head, so close they'd almost be touching, kissing.

"Any luck?" Martha asks, and Gwen shakes her head, frustrated.

"Whatever was here, it's been wiped clean. There are still a few files here and there, but nothing that makes sense; they might have been in a hurry, but they got the job done."

"Not that well," Martha says, and before Gwen can ask her what she means, she's taken Gwen's hand, pulled her towards the smaller doorway. "Come on, I'll show you."

The second room looks more like a laboratory, and whatever clean up job has been done, it's less efficient, here. There are still bits and pieces of scientific equipment; mostly larger machines, things that couldn't be moved quickly - like the computers, Gwen thinks, like whatever's on the warehouses - but a few smaller ones, too, beakers and test tubes, plus a few unidentifiable substances in containers scattered on tables.

"Take a look," Martha says, and she's sliding a petri dish under a microscope; she steps aside, and Gwen moves forward, bends down to peer through the lens.

"What am I looking at?" she says after a moment, feels Martha's hand on her back, leaning closer as she uses the other to adjust a dial. The lens zooms in, and Gwen frowns, still not sure what she's supposed to be seeing.

"It's the same as I found in that girl's blood," Martha explains, without having to be asked. "Well, sort of. Slightly different; I'm guessing this is it, before it's mixed or injected or whatever they do to it."

"Why?" Gwen asks, and it's the only question she can think of; the girl, the warehouses, the lab. There's some sort of picture here, but she can't quite see it, yet.

"Genetic manipulation," Martha says, and Gwen straightens, turning to look at her. "The girl in the warehouse, she was fast. Faster than any human being, and strong, too. My guess is, this is all part of some sort of genetic research."

"What?" Gwen asks; now that she's starting to see the picture, she doesn't like it at all. "Like, building super soldiers or something?"

"Something like that, maybe. I know UNIT's thought about it, but our science isn't really there yet. Well, that, and all the things that could go wrong."

"Like the test subjects dying," Gwen says, and it isn't a question. "That girl, she was murdered."

Martha nods, slightly, and Gwen looks away. "Her body probably couldn't take it. It would have put an awful strain on her. Human bodies just aren't meant to work that way."

"Well, we'd best get all this stuff gathered up," she says, and steps forward, towards the door. "Jack and Ianto should be finished soon, and if there are others like that girl, we'll be needing it."

She doesn't see, until it's too late, the man now standing in the doorway. Instinctively, Gwen reaches for her gun, but he's faster, prepared; he steps forward, knocks her hand away, grabs it to twist it up behind her shoulder. She lets out an involuntary gasp of pain, and she can see Martha start to move; before she can go far, there's something pressed against Gwen's arm, sharp and uncomfortable, and she turns her head just far enough to see the syringe.

"Don't hurt her," Martha says, and she's got her hands up. Gwen wants to tell her to run, wants to kick and yell and fight, but her self-preservation instincts are stronger, screaming at her not to startle the man holding her.

"We'll get out of here," Martha's still saying, edging forward, and Gwen can feel the tip of the syringe press against her a little more insistently. "Just let her go, and we'll leave you alone. Forget we were ever here."

Her eyes flicking over the man's head alert Gwen that something's going on. A second later, a sound behind them alerts her captor, too, and Gwen hears the unmistakable sound of gunfire just as she feels the needle dig into her arm, and it all goes a little downhill from there.

-

After that, everything is kind of blurry; Gwen's not sure if she passes out, except she must, because the next time she opens her eyes (and then closes them again; her eyelids feel heavy, her senses dulled except for the sharp, throbbing pain in her arm) she's in Torchwood, stretched out in the med bay.

"Gwen?" Jack's voice, and then Martha's, faint above her, and she tries to sit up. Her body, it seems, has other ideas.

"Is she okay?" Jack, again, and Gwen can hear Martha reassuring him; "... the samples we brought back from the lab. She'll be fine."

"And the others?" Jack's closer, now, and Gwen wants to reach out to him, to Martha, but her body won't cooperate.

"I'll do my best. They were pretty far gone. I'm not sure how long they were experimented on, but they're in better shape than the girl we found."

"Just do what you can," Jack says, and he's moving away from her, now.

"What about the man from the lab?"

A beat. "He'll live. He's in the interrogation room."

"What was he even doing there?"

"I don't know," Jack says, and Gwen can hear the edge in his voice, even from where she's lying. "But I look forward to questioning him."

And then there are footsteps, voices fading away, and a hand in hers; Martha's, and Gwen can feel sleep pulling her back down.

When she wakes up again, her head is clearer, though it takes her a moment to register that Martha's still there, her hand resting lightly on Gwen's shoulder. The pain is mostly gone, now, a dull sort of ache, and she smiles up at Martha's concerned gaze.

"Damn," Martha says after a minute -

I thought I was going to have to kiss you.

"- you keep waking up."

"I'm still a little sleepy," Gwen says, which is mostly a lie, and she's almost surprised when Martha leans forward, brushes her lips against Gwen's. The kiss is brief; after a second, Martha pulls back, and Gwen could almost believe it hadn't happened, except for the way Martha's smiling at her.

"You should rest," Martha says. "You'll be out of commission for a few days."

"So, nothing too strenuous, then?" Gwen asks, and she can almost believe she's talking about work.

"Not for the next couple of days," Martha says, and there's something else in her smile, now. "But you can buy me a drink."