If somebody had asked Martha Jones to sum up who Derek Reese was, she wouldn't have had to think twice about it.

"Scary," she would have said, and then, a beat later: "A friend but...yeah, scary."

But, then again, nobody would ever ask Martha that question.

Because Martha Jones had never met Derek Reese, not really.

New York was a wasteland, the stink of corpses almost overwhelming. It was said that over ninety percent of the population had died on the very first day. The New Yorkers had fought back, apparently… just like the UNIT force that the Brigadier had handpicked for Martha.

They were killed, one by one, as they'd run through Central Park, trying to protect her. The Toclafane had giggled as they counted off their kills aloud, in that sing-song voice of theirs that turned death into a nursery rhyme.

"One wee human, two…" They swayed almost drunkenly through the sky; high on their victim's fear. "Five wee humans, six…" Martha had quickly realised that they were drawing it out, prolonging their pleasure. They could have easily killed them all, in one fowl swoop, the moment they'd spotted them down in Soho.

It was their love of the hunt that had saved Martha's life.

If they'd just cut a swathe through the UNIT team, like she'd seen them do in London, she'd have died in Soho; but, alone, her back pressed against the cold brick of the bridge's underside, the TARDIS's perception filter lent her it's protection.

"It can't see me, it can't see me."

But it knew something was there. It hovered, waiting, just short of the bridge's shadow, chortling to itself. She didn't know why it didn't come in after her and try to flush her out.

Dusk had come, and she was hungry, but she daren't even reach for the ration bar in her jacket. The perception filter wasn't perfect. It discouraged people from seeing her, but it didn't make her invisible, especially to the Toclafane, who seemed to be more machine than anything else.

Martha let the tears fall silently. She's spent the last week and a half in a dark, smelly, antique submarine, getting to know the dozen UNIT soldiers who'd volunteered for this mission. They had all been young, and had come straight from the training grounds. All the soldiers with combat experience were dead or gone over to the other side. Not that it mattered, the first few days of the Master's reign gave everyone more experience than they could handle.

They still all died this afternoon, protecting her life.

I must have been crazy to think I could do this, she thought desperately. Her legs were beginning to cramp, and the rain had begun to fall softly outside. Thankfully, she had the shelter of the bridge.

A noise, like someone stumbling over a dustbin, rattled in the distance, breaking the sound of the rain, and the Toclafane gave out a cheep of inquiry. Martha held her breath as it swivelled, then rose out of view.

"Thank God," she gasped softly, letting out her breath as she crept along the wall.

And then the ground seemed to open up, and a hand caught her foot, and she tottered, falling into the darkness. A body half broke her fall, but it still hurt like hell, and a hand clamped over her mouth, as she let out a soft cry of pain...

"Pipe, down, it'll hear you," a voice said into her ear.

Martha's eyes narrowed and she elbowed her attacker in the stomach. He let out a sharp hiss, but didn't let go.

"Listen, you stupid bitch, I'm trying to save your life here. Don't make me regret it."

Martha's hackles went up, and she promptly stomped down on his foot. She hated that word.

"Ooof—" This time, he did let go, and Martha backed away, her eyes adjusting to the near utter darkness. She was in some sort of sewer system; the clammy touch of the wall under her fingers told her that. Plus, she remembered what they looked like from the last time she'd run through them.

She felt a pang; for herself, for the Doctor, for a life that was gone now.

A shadow crouched near the manhole, and Martha felt her throat go dry. She still couldn't make out his features. "Don't come near me or I'll…I'll…"

A humourless laugh. "Or you'll what? You'll stand really, really still and hope I don't notice you?" he drawled, mockery evident in his voice. "You're obviously not armed, so save it."

"You've been watching me," she said warily.

"More like I've been trying to stay out of the firing line," he countered. "What were you thinking— ssh!"

A whirr sounded softly from above, and Martha felt her mouth go dry, as the light dimmed even further, blocked by the shadow of the Toclafane. Martha froze, and watched as the stranger melted into the shadows.

"I can see you," the Toclafane carolled. "Come out, come out."

Martha held her breath, even as she wondered why the Toclafane didn't just come down after them. It spun, and whirred mid-air, just above the manhole. Did it really expect her to come out and let it kill her?

"Nowhere to run, Martha Jones," the Toclafane said. "Mister Master wants you, and you'll be his." And then, with a pop, it disappeared.

The stranger cursed under his breath. "Great, just great," he said, as he swung up onto the manhole ladder and closed it.

"It's okay, it's gone," Martha said.

"Not for long," the stranger said grimly, as he clicked on a torch, and drove a bolt home on the manhole… a bolt?

"Since when do manholes have bolts locks?" Martha asked.

The stranger gave her a look, as if she'd asked why was the sky blue "We'll need to move fast," he said. "They won't come down here on their own, not anymore, but they will travel in packs, and we'll want to be somewhere else when that happens."

"We do?" Martha's eyes had become accustomed to the light of his torch. He was tall, wide shouldered, and moved like he'd been doing this for years. "You're military?" she asked.

He looked at her. "It knew your name," he said. "I've never heard one of those things call a human by its name before."

Martha sighed wearily. "Yeah, it's a long story."

"Is it the kind of story that's likely to get me killed?" he asked. He grabbed Martha by the elbow and steered her down the sewer tunnel. Martha let him; it wasn't as if she knew where they were going. Which reminded her…

"Where are we going?"

"You'll know when we get there," he said tersely.

"Why won't you tell me now?"

"So you won't blab if we get caught before we reach it."

Martha swallowed, as she realised what he was saying. He didn't want her to know just in case she was tortured or, worse, a collaborator. There had already been talk of those even before she'd left Britain, a scarce few days after the Master's rise to power. The tunnels seemed to go on forever, and Martha began to suspect he was taking her the scenic route. It knew your name, he had said. She guessed he thought she was a collaborator.

"Stop," he said. They had come to a shallow recess in the sewer wall, and Martha raised an eyebrow as she saw the metal door. He rapped on it once, then twice, then five times; it creaked open, and an elderly woman's face peeked out.

"A new one?" she asked, her Brooklyn accent showing sharply as she gave Martha the once over. "Not like you to bring in strays, Reese."

Her would-be-rescuer, who now had a name, grunted noncommittally as he shouldered the door, and the woman sighed as she gave way. "Where's Aaron?" she asked, as she peered into the darkness, beyond Martha.

"He didn't make it," Reese said sharply, as he pushed Martha inside before him.

The elderly woman let out a long, strangled breath. "They spotted him?"

"He got caught in crossfire," Reese said bluntly, and Martha's mind went back to what he'd said when she'd accused him of watching her. That he'd been trying to stay out of the firing line. With a sinking feeling, she realised exactly what had happened to Aaron.

"Reese—" the lady said.

"I know, Liz," he said. "I'll make another run."

And, in the dim light, Martha made out the faces peeking out from makeshift tents made out of cardboard and blankets, spread across what looked like a warehouse with no windows. "What is this place?" she asked softly.

"They're storage rooms for--"

"Liz," Reese said, warningly.

Liz's eyes widened as she looked at Reese, and Martha's heart sank as she realised she'd been right. He thought she was a collaborator.

"There will be a hunting party, pass it on. They'll come looking soon."

Liz nodded, and bustled down the corridor. Two shadows peeled from the wall and followed her, and Martha realised that they were the faces she'd have seen at the door if Reese had given the wrong knock.

"Come with me," Reese said. They passed through a curtain made of blankets, which blocked off a corner of the room and, suddenly, Martha found herself slammed up against a wall. "It knew your name," he said flatly, without preamble. "Tell me why."

Martha felt her lips go dry. "I'm a friend of the Doctor, and the Master thinks I'm going to try and rescue him," she said. No point in lying. After all, wasn't that what she was here for? To spread the word?

Reese gave a snort of disbelief. "You?" he scoffed. "Rescue someone from the clutches of that maniac?"

"That's what he thinks."

"Listen, honey, I saw you out there. You'd be lucky if you managed to rescue a strangled kitten."

"Oy!"

He plunged on. "What were you, before this happened – a teacher, a secretary?"

"Trainee Doctor, if you must know."

"Really?" He gave her a speculative look. "That might actually come in handy."

Martha snorted. "So glad you approve—"

"Is he right? Reese asked abruptly. "Are you going to try something stupid, like rescue this Doctor guy?"

Martha bit her lip. "It's a bit more complicated than that."

"Yeah, something told me it would be. It always is."

He backed off, and Martha breathed a sigh of relief. "I'm not going to rescue him; it's the other way 'round," she babbled.

"Oh, for…." He took a deep breath. "We're thinking about the same geezer, right? The guy the Master turned into a pensioner on live TV?"

"Don't you think I don't know how crazy this sounds?" Martha said, exasperated. "But he's the only chance we've got."

"Bit too late for that, kid," he said. "All we have are corpses on the ground." His voice was harsh, unrelenting.

"And what if I told you the Doctor could change that? That he could turn back time?" Martha blurted out, on impulse.

Reese grew still, his eyes blanking. "What if you did?" he asked, his voice curiously intense. Martha shivered, as he pinned her with his eyes. There was something there that she'd never seen before. Oh, she had sometimes seen hope in their eyes, and maybe even belief, but not this…

"You know," Martha whispered softly.

He turned away and shrugged out of his jacket, throwing it onto the bed. He took his gun out of its harness and dropped into a sitting position on the floor. Martha noted the weapons that littered the tiled surface around him.

"So, you're military, yeah?" she asked, unsure, as he silently started to pull apart the gun. What was he thinking? Was he cleaning the gun so it would be all nice and shiny when he killed her?

Click

"Were you UNIT?" she ventured. It would explain why there was no doubt in his eyes when she mentioned turning back time. The Brig had told her about the Doctor's time with UNIT.

Click

"Not UNIT, then," Martha sighed. "Navy?"

Click

"Canadian Mounties?"

He stopped, then looked at her silently from amidst his pile of armaments. The picture was simultaneously really freaky, and strangely reassuring. "I don't like to talk about before," he eventually said.

"It was a joke," Martha said softly. "About the Mounties."

His expression didn't change. "I know that," he said flatly. "Sit down."

"What?"

"Sit down, here, beside me."

Martha looked at him warily, and then cautiously sat, cross-legged, on the floor beside him. He wouldn't kill her in his personal space, would he? It would make too much of a mess... yeah, right.

"So…what now?" she asked, grimacing as she heard the shake in her voice.

Reese picked up a gun and dropped it into her lap. "That is an AK47. It's a machine gun, a semi-automatic to be more exact, common as muck but fairly reliable—"

"I don't use guns," Martha said automatically.

He looked at her coldly. "Cute," he said. "Look around you, honey. You may not be armed, but everyone else is. You know why? Because it's kill or be killed out there, and unless you're expecting someone else to do your killing for you—"

"I don't expect anything from you," Martha said, as guilt rose up inside her. It was an emotion she'd become very familiar with, of late.

He looked at her, as if she was a leaky faucet he had to fix. "I'm going to show you how to pull apart and clean a gun," he said. "And then I'm gonna teach you how to load one, and point one." He threw her a rag. "And then, after that, I'll show you how to kill someone with it… start with the clip."

Martha looked at the rag in her hand. "I don't understand. Why are you doing this?"

"It knew your name, kid," he said. "That means you, and everyone who is around you, is in immediate and terminal danger; no reprieves, no second chances. You've gotta know what to do if your life is at stake because, from what you've told me, more than your life rides on it."

Martha looked at the gun on her lap. It seemed to grow even heavier as he spoke. "Martha," she said softly.

"What?"

"My name is Martha, not kid," she said. "Use it, or I'll start calling you Butch."

Was it her imagination, or was that a glimmer of a smile? "Tell you what," he said. "You start shooting like Sundance, and I'll call you whatever the hell you like."