Martha came to a sudden, unannounced stop, nearly tripping him up.

"What?" he said, looking down at her. "What is it?"

A strange, detached look had fallen over her.

"I don't want to leave," she said, and tried to tug her hand from his.

He held firm. "What?"

"I'm not going with you."

"Martha, don't be ridiculous."

"I'll scream if you don't let me go."

He stared at her hard. And then allowed a slightly crooked, rather unnerving smile to surface.

"Well, hello you," he said, eyes traversing over her. "I was wondering when we'd meet again."

Her eyes narrowed. "I beg your pardon?"

"You can stop that, now," he dismissed. "There's no point." Abruptly, he grabbed her chin, tilted her head to the right, and ducked forward to give the left side of her neck a close sniff. "It is a bit stronger now that you're in the driver's seat, I reckon."

She turned her head back to fix him with a sharp look. "Sorry?"

He ignored the query and manually turned her head again, cold nose hoovering over the other side of her neck, snuffling around her jugular. When the sniffing progressed to her armpit she took a step back, shoving him away hard and glaring.

"Hmm," he murmured, nodding decisively. "That is clever. I mean, not nearly clever enough, not by half, but still." He gave her a short, patronising round of applause. "Very seamless, I'll give you that. Although you've rather showed your hand now with the stunt in the toilet, wouldn't you say?"

"I have no idea what you're on about."

The Doctor peered at her carefully. "If you can hear me," he said, "blink."

"What?"

"Not you," he snarled, anger sharpening his tone, voice raising. It was startling enough a change to make her flinch back and gasp involuntarily. "I'll deal with you in a moment. Martha." His voice softened and he searched flat eyes. "I need to know you're still in there somewhere."

She stared at him coldly.

"Very well," he said, sighing heavily, putting his hands on his hips. "You want me to spell it out for you? You've been caught out. Rattled. Sussed. I was onto you seconds after you left." He scoffed, shaking his head. "Martha never would've done anything that you have tonight, not in a million years. And even on the very slim chance that she did, there's one gaping flaw in your plan. Did you never consider that I might just like her perfume?"

The confusion on her face twisted. "My… perfume?"

"Cinnamon and sandalwood. Faint notes of vanilla. Hint of citrus in there." He fluttered his fingers like a conductor. "Lovely. Distinctive. Smelled it everyday for half a year now."

"Yes," she said impatiently. "And?"

"And it may just be a coincidence, bit of an oversight on my part, but all those hundreds of times I've smelled her perfume," he continued blithely, eyes digging into hers, "I never once noticed traces of vorax and ceranium."

His expression was sunshine and smiles as hers darkened, losing all remaining trace of faux human emotion.

"Brilliant," he said with mock cheer. "Now we can have a real conversation, you and I, without having to pretend I'm unaware that you're using my friend as a hand puppet. Let's start with introductions." When he smiled, teeth bared, the expression entirely failed to reach his simmering eyes. "I'm the Doctor. And you are?"

He didn't know what he expected, precisely – some grandstanding and threatening and general menace, perhaps. But it was not for her to turn tail and bolt.

It startled him so much he almost didn't catch her. Fortunately, his strides dwarfed hers, and he recovered from his surprise in time to grab her before she could flee back into the club.

Her mouth opened with a giant gasp to shriek; he clamped his hand hard over her lips. She thrashed, kicking violently as he hauled her back to his front to detain her.

"That's not going to get you anywhere," he sighed, dodging the heels of her boots and dragging her backward through the corridor.

"Let go!" he heard, lividly muffled beneath his palm. She reached up and dug her nails into his wrist, struggling to yank his hand away from her mouth. They pressed harder and harder, clawing into his skin until there was a warm splitting sensation under her grasp, and slickness against her nailbeds.

The Doctor didn't so much as flinch. "Are you quite finished?" he said, sounding rather unimpressed.

At his complete non-reaction, there was a flicker of uncertainty, a hint of disturbed puzzlement across her face. She looked down and blinked at the sight of the blood welled under her fingernails, seeping into his cuff.

"You can do anything you want," he told her. "Kick, scream, scratch, take my eye out. I'm not letting you go. You've hurt a very good friend of mine tonight. And that isn't something anyone in this universe gets away with."

She dug her nails in harder, growling in frustration, trying to break from his grasp by writhing side to side.

"Bear in mind," the Doctor added quite calmly, still carrying her backward toward the door, "if you do any lasting damage to that body, you will live to regret it. So let's go easy on the contortions, shall we?"

His back hit the push bar, and he dragged her out into the night, into the alleyway.

"Help!" Her voice strained through his fingers. "Help!"

And there was a nearby stirring of movement.

"Oi," said a male voice. "You."

The Doctor stopped, at the absolute limit of his patience, and turned to face the bulky figure emerging from the shadows.

It was a bouncer, off duty – a cigarette hanging limply between his lips as he pushed off the brick wall and unconsciously stood in the path of the TARDIS.

"Hands off," the man said tiredly.

"While I appreciate the sentiment," the Doctor retorted, keeping an iron grip on Martha, "I'm afraid this is a bit outside your purview."

"Look, I just got off my shift. I don't want no trouble with you." The bouncer let out a smoky exhale, running a hand over his close-shaved head. He reminded the Doctor somewhat of Mickey, in his face and eyes – although this particular gentleman easily could have been three or four Mickeys taped together.

"I don't want trouble either," said the Doctor. "Completely trouble averse, I am. Glad we're agreed, lovely chat. Don't suppose we can go our separate ways, now?"

Martha's body pulled aggressively against his arms. He looked past the massive obstacle in his way to the TARDIS, teeth gritting. He had to get her into containment as soon as possible, before someone else died. Before the thing jumped bodies and set itself loose upon Earth.

"Come on, mate," the bouncer groaned, looking quite annoyed. "What do you get out of this? You're good-looking enough. There are plenty of birds in there that'll jump to do whatever freaky shit you want. Just let the lady go if she's not interested."

Suddenly, the Doctor felt the resistance in his grip lessen. Martha stopped fighting him as the bouncer strode closer, staring at the impending man with sudden interest.

He'd seen that bottomless look in her eyes right before disaster had struck in the TARDIS – and swore inwardly.

"Don't come any closer," he warned the man, tightening his hold on his companion.

The bouncer glanced pointedly between himself and the Doctor, silently indicating the four inches of height and seventy pounds he had on the Time Lord without a single word. He folded both heavily-tattooed arms across his broad chest and raised an eyebrow. "What, you armed or something?" he asked, looking entirely unconcerned, continuing to stroll forward.

"It's not me you need to be worried about. Please. It's for your own good."

But it was too late.

As he came within proximity, the bouncer's irritable stare fell, quite precipitously, from the Doctor to Martha.

She went entirely lax in his grip, peering up at the large man, eyes innocent and inviting. Still breathing heavily from the exertion of fighting against him – and, he suspected with a flush, from other activities – she reached out one of her arms out to him.

The bouncer dropped his cigarette on the asphalt. And from a purely scientific standpoint, the Doctor was fascinated at how efficiently it worked. He could practically see the lights shut off, rational thought powering down, coherence giving way to instinct. The man staggered a jerky, lumbering step closer, eyes lidding. He licked his lips, and then suddenly extended one massive hand, as though to pull her away from the Doctor.

"Sorry to interrupt a touching moment," he announced loudly, tugging her away with a heave, breaking the spell as he lifted her off her feet. "But there will be no more of that this evening."

She protested in the expected violent fashion, kicking and struggling. "Let me go," she demanded, and in a moment of unique rage, bit his thumb.

"Martha!" he shouted. "I know you're not yourself right now, but… come on! Teeth?"

For his part, the bouncer stumbled back. He looked shell-shocked and flustered, all at once.

"The hell was that?" he demanded. Awkwardly, he adjusted his belt, taking another unsteady step backward. "How – what—"

"I told you," said the Doctor, grunting as he tried to subdue his fighting companion. "It's not me you need to worry about. Please, just get out the way. I need to help her before she hurts someone else."

"But how…" The man, bewildered, seemed to process the scene from a different angle. The deep, bleeding fingernail crescents in the Doctor's wrist – the fresh bite wound on the heel of his hand. The resounding lack of any injury whatsoever to Martha as she stomped on his toes. The strange, almost inhuman lack of emotion in her eyes.

"What the hell kind of weird shit is going on here?"

The Doctor sighed heavily. "You know what?" he said. "You seem like a reasonable man – I didn't catch your name?"

"Harold," the bouncer supplied, a bit numbly.

"Harold, you seem like a reasonable man. And I've had a really long night, so for once I'm not going to obfuscate or lie or show you the psychic paper or wipe your memory or temporarily blind and deafen you with a sonic pulse—"

"What?" he sputtered.

"I'm going to do something I don't often do, instead." With that, the Doctor hauled Martha past the dumbfounded man, toward the TARDIS, fishing his key from his pocket. He held it in his mouth briefly as he got her securely pinned against the box, and then unlocked it and unceremoniously kicked open the door. "I'm going to tell the truth."

Harold gasped.

"Yes, it's bigger," he sighed blandly, and pushed the small woman at his side in, slamming the door before she could shove past him. At his psychic direction, the TARDIS sealed itself with a soft metal snick, the lock shuttering closed.

He turned to meet the other man's panicked gaze as fists began to pound on the opposite side of the door.

"No, it's not an illusion," he answered, before the question could be asked. "It's a time machine which I stole quite some time ago from my home planet. My friend is human, but unfortunately, her body is currently being inhabited by a malignant alien force of some sort. Haven't pinned down which yet, but tonight, it used her to kill a man in a rather unpleasant – er, depending on your perspective – manner inside your club. I do appreciate your concern, but she's going to be all right. I'll put her into containment and find a way to extract the alien from her body. Whatever it takes."

The man stared, face blank. And then, at last he spoke, voice flat with disbelief: "You stole it?"

The Doctor blinked. "Really? All that, and that's what sticks with you? Blimey, Harold."

"What have you done?" Martha's voice shouted from inside.

Harold peered warily at the TARDIS. "Did she drug me, your girl?" he asked. "Is that why I'm seeing this? Am I high?"

"Well, she did drug you in a… manner of speaking, yes. But it's nothing that won't wear off. I assure you everything you're seeing is firmly rooted in reality. Still, you might feel a bit… erm, volatile, for a little. Probably best you just go home and sleep it off."

"Go home," he muttered, rubbing his face. "Sleep it off. Right."

"You're taking this well," the Doctor commended him. "Most people would be breathing into a bag by now. The ones that don't..." He frowned back at the door as it rattled under his back. "Actually, I can't say it turns out well for them."

"I thought you were just some arsehole roughing up a lady for no reason, and…" He lost his words, shaking his head at the TARDIS. "I mean, I s'pose I shouldn't be surprised, should I? What with the spaceship crashing into Big Ben, the Christmas star. That… Sycorax lot." He paused. "My wife was on the roof of our flat building. Dunno know why I'm even shocked."

"Attaway to keep an open mind, Harold."

He rubbed his temples. "I just guess… bloke with a weird girlfriend in the back alley behind my job, is somehow harder to swallow than evil overlord in the sky."

The Doctor managed a slight, exhausted smile. "I imagine it'd be less awkward if I started shooting lasers and declaring my dominion over humankind, eh?"

"Actually, yeah, it would," Harold muttered. And then he pressed his hands over his face again, regarding the TARDIS with dismay. "Jesus Christ. I was just having a smoke next to that thing. How did I not notice it was there?"

"Oh, she doesn't mind," the Doctor said, patting the side of the TARDIS. "She's very discreet."

"And I can't believe I was actually going to try to knock you out. I could've gotten… I don't even know. Melted. Incinerated, just by touching you."

"I don't typically tend to go around incinerating people at the touch, so, no worries there. You'd likely have pummelled me. But then Martha, my friend, would have gotten away, and the thing inside her would've killed God knows how many more people – probably starting with you, as a little thank-you for its freedom. So cheers for holding off on the knocking out. It's a pleasant change of pace, people not beating me up when I'm trying to help."

The pounding on the door finally ceased, replaced by a tense and worrying silence.

"What did she do to me?" he asked, rubbing either side of his neck. "I mean… Jesus, that was weird. She's hot and all, mate, but – I'm married."

The Doctor scrubbed a hand down his face and gave a haggard sigh. "I don't know why, but the alien inside her seems to be after… well, exactly the sort of thing that would make you conveniently forget that you're married."

Harold got a rather embarrassed look about him and adjusted his belt again. "You mean…"

"Afraid so." He shook his head and grimaced. "It's not your fault. The thing's amplified the normal potency of her pheromones by about five hundred percent – it gave off such a strong biological signature that I used to track her down. There was nothing to stop it from altering your brain chemistry, once you came too close. It must've affected the man that was killed in the same way. And the only reason it doesn't affect me is because, thankfully, I'm not human."

"Damn," remarked Harold. "That's fucked."

"My sentiments exactly," the Doctor sighed. "When the alien went after that man in the club and harvested the, erm… collectively built energy, it seemed to be such a violent process that – as far as I can tell – it atomised him on, er… arrival. I mean, we're talking, just: poof. Gone. He was literally dust. Never seen anything like it."

"So, you're saying… he got off, and then he…?"

"The turnaround was near instantaneous. I didn't have time to do anything. I couldn't save him."

Which wasn't entirely truthful, as the Doctor had been rather less concerned with saving the man's life in that moment than he'd been on ending it himself. But he figured those particulars weren't relevant to the tale.

"Sheesh. A shag to die for." Then his face changed, with a disturbed realisation. "Christ. That must have been hard, seeing your girl like that, with some… I mean, even if she was, you know, possessed."

The Doctor frowned at him for a moment, opening his mouth to respond – then closing it without a word, shoving his hands deep into his pockets and looking uncomfortable.

"Sorry," Harold said quietly. Then he looked to the TARDIS door. "She's gone awful quiet in there, hasn't she?"

"I was hoping it was just me," the Doctor sighed.

"You probably ought to go… handle that."

"Yes, I probably ought." He held the man's eye. "You've been an excellent sounding board this evening, Harold. Thank you."

He stuck out his hand. Harold regarded it warily for a second, then tentatively shook the tips of his fingers as though they might've been contaminated. "Yeah," he said, sounding reluctant. "You're welcome, I think."

"I trust I can count on your discretion?"

Harold raised his eyebrows. "Nah, let me run inside and tell management an alien killed a bloke by possessing a pretty bird and shagging him to death. And oh, by the way, now it's hiding outside in a different alien's time machine."

"You make a strong point," said the Doctor, giving half a smirk. "On second thought, blab away."

The bouncer shook his head and turned away with a mild groan. "Fuck, I need some sleep."

"Not so fast," the Doctor chided. "You don't wanna miss the best part, do you?"

"God, it gets worse?"

With an upraised eyebrow, the Doctor cracked the TARDIS door and backed inside. "You'll see," he promised.

He closed himself in, then turned around to see Martha sitting upright on the jump seat, watching him with murder in her eyes.

Ignoring it, he casually strolled to the console and tossed the handbrake. The TARDIS gave a whooshing, achy groan and began to dematerialise.

He glanced at the monitor. On the fuzzy screen he saw a large figure in black gape at the disappearing time machine, before throwing up its hands in exasperation and storming away. He suppressed a smirk and switched the screen off.

Then his gaze turned to the woman sitting on the other side of the TARDIS.

"Well," he said to her, gesturing expansively. "You know how it goes. Easy way, hard way – all the rubbish in between. What'll be your preference this evening?"

Her eyes narrowed into a biting, determined glare.

He sighed. "As you like."

The body of Martha Jones sat motionless on the floor, gaze fixed, knees drawn to her chest.

"You can't keep me in here," her voice stated flatly, disinterestedly.

The room was warm and winding, branching and organic, but the sickbay contained something that other identical spaces in the TARDIS did not: a cell.

Partitioned off by glinting, double-walled Perspex, there was a round corner of the asymmetric room that was not cluttered and craggy but barren and sleek, flooded with harsh aqua fluorescence. There was nothing inside but a blanket, a book, and a hard coral slab doing its best impersonation of a cot. Outside the enclosure, just by the glass, was a brass wall panel labelled with concentric circles. Beneath the panel was a smudged, Sharpie-drawn arrow to the circular script, with a centuries-old English translation scrawled as an afterthought: QUARANTINE.

Under that, parenthetically: FOR CONTAGIOUS STUFF.

"No," agreed the Doctor. At a small desk heaped with stray medical implements and loose paper, he was perched on a stool in profile, hunched over its surface. Shirtsleeves were hiked to elbows, a bottle of antiseptic on hand as he silently tended to the scattering of furious red wounds raked along his hands and forearms. He didn't look up as he spoke. "I don't suppose I can."

"There's nothing you can do. No antitoxin. No clever machine. Anything powerful enough to expel me will, in turn, kill her." A self-satisfied chuckle arrived, and in it, there was a strange, unearthly, almost synthesised bass in it, hidden just underneath the pleasant human voice – the creature within, shining through, gleeful in its taunt. "You pursue a remedy in vain, Doctor."

"Only thing I'm pursuing right now is some Neosporin," he reported flatly – and hissed out a mild curse as he swept over a particularly violent scrape. "You certainly put up a fight."

There was a moment of terse silence.

"So," the voice was morphing into a drawl of low sarcasm, and the Doctor's jaw clenched at the imitation of Martha, "you're doing nothing."

"Looks that way," he said evenly.

"She'll die."

He shrugged, unearthing a dusty box of plasters from nearby. "Happens to the best of us, I'm afraid."

More silence. Hands clenched and unclenched.

"I need the energy." There was bitterness, sharp and furious, suddenly infusing the voice. The Perspex thudded dully as her hands and face pressed against it. "I need it. Not you. Not this body. I'll find another — I don't need her, I need the energy." Distant longing settled into her voice, then. "In the whole of the universe," she breathed, "there's no hit like it. Orgasmic energy…the build-up, the release…"

"You've said," he interrupted sternly. "Repeatedly. I'm not letting you go. Do you really think I don't know what'll happen if I do?" He shook his head and scoffed. "I'm not bargaining her life so you can go take countless others."

There was a furious pause. He could hear the sound of small impatient feet, pacing.

"She'll die."

"You're beginning to sound like a broken record," the Doctor noted. "Never reuse threats when you're negotiating, that's How to Hold Hostages 101. People might stop taking you seriously. Next thing you know you're handcuffed, facedown in the back of an armoured van with Judoon reading you your lack of rights." He frowned. "Not that I'm speaking from experience, mind. I mean, it was all a misunderstanding with a Zygon in a bank. Got sorted in the end."

"She's dying right now." He felt eyes on him, intent, unflinching. "Without energy, this body won't last much longer. A day. At best."

He rolled down his sleeves gingerly, buttoned his cuffs, and stood from the table, pulling his jacket from the back of the chair where it draped. For the first time since he'd wrestled her through its door, he looked directly into the quarantine cell, meeting her eyes through the glass.

For an on-edge moment, they regarded each other, silently analysing.

And then the Doctor slung his jacket over his shoulder and sighed. "You hungry?" he asked.

Martha stopped in the middle of the cell, staring at him disbelievingly for a beat. Her shoes were thrown angrily into a corner, and she stood barefoot in her jeans and tank top, slightly sweaty, wild eyed.

"Hungry?"

"There's no need to shout. I know it's an icky corporal thing, hunger – but this clearly isn't your first go-round in possessing an organic sentient being. Given all the other things you've had time to get up to, I'm sure you know what a tummy rumble feels like at this point."

Another silence: this one, deeply suspicious. Even as drained, robotic and lifeless as they'd been made, he knew those eyes. He could read the hesitancy in them in an instant as they searched his.

"You forced me into a cage," she said eventually, voice hard. "You don't care."

"About you? Not a whit. But you've taken over the body of someone I do happen to care about – someone who could still be in there – and I want her to be as comfortable as possible. Especially given the circumstances." He raised an eyebrow. "So, I'll ask again. Are you hungry?"

She took a step back from the glass and folded her arms, stubbornly silent. And he'd known that sullen face, that particular stance – shoulders square, jaw tense, one hip jutted out just so – for plenty long enough to know what it meant.

"I'll be back with a sandwich."