Filling a room with gas and lighting a spark with only seconds to get himself out of the blast zone hadn't been one of the Doctor's most brilliant plans, but he was desperate for anything that might slow Lazarus down.

Unfortunately, it had done little more than aggravate the monstrosity, and the Doctor continued dashing through the building trying to make his way back to the demonstration hall.

With any luck, it would be empty, and he could use the larger space to put some distance between himself and Lazarus. Keep a room's distance between them so he had a chance to think of a plan.

Hopefully, a plan that ended up with Lazarus as a harmless human, and himself not regenerated.

One left, then a right, then another right and—

"Oof!" He spluttered, hands lifting to grasp at Martha's arms, stopping the both of them from going flying as they collided in the hallway.

"What are you doing here?" He asked, eyes checking her over quickly for injuries, but the young woman just grinned and held up his sonic.

"Returning this," she announced, "thought you might need it."

He took it from her, but frowned quickly "Where's Rose? And how did you—"

"Heard the explosion. I guessed it was you," she answered quickly, before he'd finished asking how she'd found him but he noticed that she'd ignored his first question entirely.

"I blasted Lazarus—" he started to explain, and Martha's face lit up with hope.

"Did you kill him?" She asked, and the Doctor instinctively glanced behind him at the question, grabbing her hand when he saw the mutation appearing at the end of the last hall he'd run down.

So much for his head start.

"More sort of annoyed him," he groaned before tugging on her hand and taking off running again, keeping hold of her so she didn't get left behind.

"How'd you get the sonic?" He asked as they ran, "Where's Rose?"

"She gave it to me when she came back inside!" Martha cried as she skidded around a corner after him, his grip on her hand helping her stay upright, "I thought she'd have found you by now."

The Doctor growled at her explanation, not bothering to mask his frustration.

"How did I manage to forget just how jeopardy friendly she is?" He muttered to himself. He could see a grin briefly flash across Martha's face, but it disappeared quickly when they heard Lazarus let out a fresh roar from far too close behind them.

They ran back into the main room and the Doctor ground to a halt, eyes flying around the room as he searched for the threads of a plan. An idea. Any idea. Especially if it included a small blonde human.

Nothing sprang to mind, and Rose didn't appear, and the Doctor ran his hands through his hair in barely restrained frustration.

"What now? We've just gone 'round in a circle!" Martha cried.

"We can't lead him outside," the Doctor muttered and turned to grab her hand, guiding her across the room quickly. He needed time to think, and the only place to hide that Lazarus wouldn't immediately follow was inside his precious creation.

"Come on, get in!" He hissed quickly, tugging the door open and shoving Martha in ahead of him.

He heard a yelp of surprise, but just followed her in quickly pulling the door closed behind himself firmly. It didn't look like Lazarus' knew form had hands dexterous enough to pull the door open, and he was banking on the fact that, even as monstrous as he was, Lazarus wouldn't want to destroy his life's work.

At least, not immediately.

"Where the bloody hell have you been?" Rose's welcome voice from behind him, and relief flooded him as he tried to turn around, managing to elbow her in the side and stand on Martha's foot in the process.

"Where have I been? What about you!" He demanded, but he was grinning at her, and the small blonde rolled her eyes.

"What are we doing in here? Are we hiding?" Martha whispered just as they heard Lazarus crash into the room, his growls echoing loudly just outside the capsule they were trapped in.

"No," the Doctor answered softly, "he knows we're in here, but this is his masterpiece. I'm betting he won't destroy it, not even to get to us."

"But we're trapped," Martha said slowly, her voice hardening and the Doctor cleared his throat, nervous about the irritation in her eyes.

"Weelll... Yeah... That's a slight problem."

"You mean you don't have a plan?" Martha asked, her eyes widening and to his horror Rose openly snorted with laughter.

"He never has a plan," she teased, and he spared her an offended ook, before huffing softly.

"The plan was to get inside here," he explained, shooting the humans the 'you've-dribbled-on-your-shirt' look that he'd perfected back in his second regeneration.

"Then what?" Rose asked him innocently, too innocently, and she had an eyebrow raised that told him he wasn't as impressive as he thought he was.

Rassilon, he wanted to kiss her.

Fighting back a flush at his thoughts, he spluttered over an answer that wouldn't prove her entirely right and tried to focus.

"Then... Then... Well, then I'd come up with another plan!" He forced out, falling silent as Lazarus' shadow passed around the capsule as he circled them. Each step he took made the ground tremble, and Martha swallowed her fear back, audibly.

"In your own time, then," she growled at him and the Doctor glanced back at Rose, frowning.

"Hang on, what were you doing in here?" He asked, and she sighed.

"Trying to figure out how this worked. Seeing if I could reverse the process somehow. Change him back, or—"

"Brilliant!" The Doctor cut her off, and glanced down at their feet, a small panel had been pulled up, exposing a series of colourful wires and he beamed.

All he needed was his sonic and about thirty seconds, and he could...

He shifted and tried to lift his arms, to twist for the device, and the two women were staring at him before he sighed and reluctantly gestured for Rose to help.

"Rose, could you just... The sonic, it's inside my jacket..." he waved a hand at his own chest and she rolled her eyes before diving her hand into his pocket without hesitation, bold enough to make him grin down at her.

She pulled it out quickly, sliding it into his hand without comment, and he cleared his throat.

"What are you gonna do with that?" Martha asked as Rose shuffled back from him, pressing herself as close as she could to the wall of the capsule and giving him room to work.

"I'm going to improvise," he told Martha, trying to inject as much enthusiasm into his voice as possible, while Lazarus continued to climb all over his invention, still seeking a way inside that wouldn't destroy his life's work.

Slowly, and trying not to jab an elbow or knee into Rose or Martha, he slid down the inside of the capsule and crouched over the wires that Rose had already started working on.

He spared a moment to cautiously evaluate the device, quickly figuring out how it connected together, and what his favourite pink and yellow human had changed.

She'd been on the right track, but Rose had been working with conventional tools and hadn't got very far into the needed adjustments, he noted, spotting the miniature set of tools on the floor between her booted feet and he grinned proudly to himself, before spinning the sonic between his fingers and continuing her work.

"I still don't understand where that thing came from. Is it alien?" Martha asked from somewhere above him, and the Doctor shook his head.

"No. For once, it's strictly human in origin."

"Human? How is that human?" Rose demanded, and the Doctor let his mouth answer on autopilot as he focussed on rewriting the device they were standing in.

"Probably from dormant genes in Lazarus' DNA. The energy field in this must have reactivated them, and now it looks like they're becoming dominant."

"So it's a throwback," Martha simplified, and he nodded.

"Some option that evolution rejected for you millions of years ago, but the potential is still there. Locked away, and forgotten about in your genetic makeup, until Lazarus unlocked it by mistake. Nice shoes, by the way."

"Thanks," both women answered simultaneously. There was a beat of silence before Rose giggled, and Martha quickly followed, chuckling softly, and the Doctor grinned. If they could laugh together... but now wasn't the time.

The lights turning on inside the capsule silenced their soft amusement, and Rose swore under her breath, the Doctor echoing her sentiment silently.

"Please tell me that you sonicked the wrong wire?" She pleaded, but he could tell from her voice that she knew it was a futile hope. He'd have warned them about that, but he clenched his teeth and kept working, the sonic buzzing away in his hand.

"Doctor, what's going on?" Martha demanded, but his silence had tipped Rose off and she swore again.

"Sounds like he's turned the machine back on," the Doctor finally admitted, and he heard a soft thunk, eyes lifting just briefly enough to see Rose with her head tilted back against the wall of the capsule, eyes closed.

"That's not good, is it?" Martha asked, and the Doctor sighed, turning back to the next wire he needed to adjust.

"Weelll... I was hoping it was going to take him a little bit longer to work that out," the Time Lord admitted. Honestly, he'd been hoping Lazarus' new body wasn't capable of it, but he wasn't going to admit to relying that heavily on hope for their escape.

"I know he's not as smart as you, Doctor, but he is a genius," Rose muttered. Torn between pride and sheepish embarrassment, he stayed silent, letting the growing hum of the machine around them sharpen his mind.

The rings of light were beginning to pulse over the capsule, and he could feel panic clawing at his senses. He would not lose Rose again. Not this soon. Not now. Not because he couldn't reverse the polarity fast enough.

He could hear Martha's panicked breathing, could see her shifting her weight on her feet, but Rose was still, almost calm.

"I don't want to hurry you, but—" Martha pleaded, and he growled.

"I know, I know! Nearly done!"

"Well, what're you doing?!" Martha snapped, her fear crackling through her voice and he answered on autopilot, his attention focussed on the machine and not stopping his mouth from running.

"I'm trying to set the capsule to reflect energy rather than receive it."

"Will that kill it?" Martha demanded.

"Maybe," Rose answered, and he let her, using the distraction to focus again.

"It's simple math," Rose continued, "transformed, he's around three times the size he is as a human, so his cell density is weakened. Like butter over too much bread."

The Lord of the Rings comparison might have made him laugh under any other circumstances, but he didn't have time to laugh and, frankly, it was a pretty accurate description.

"With a little bit of luck, the energy blast from this thing could separate the cells. It should at least do him some damage—"

"If I can get it to work," the Doctor growled, but without Rose's calm explanation, Martha was losing her grip on her panic again.

"We're gonna end up like him!" She screamed, and the spinning columns of light were nearing full velocity, becoming a blur of solid motion outside the capsule as the whirring hum of the electronics filled the space, deafening them all.

"Just one more!" The Doctor shouted. He doubted either of them could hear him over the machine, but Rose's hand settled on his shoulder, her touch light and trusting and the tension drained out of his shoulders as he reconnected the last filament.

The machine erupted, a shrieking scream of metal and electronics shook the machine, and the light exploded, near binding them, but it had travelled out and away from the capsule, just as he'd intended.

There was a loud crash as it connected with the creature outside in the demonstration hall, and the sudden silence was almost as painful.

"Oh god, I think my ears are bleeding," Rose moaned softly, and her hand left his shoulder.

He slid to his feet slowly and found her with her fingers pressed to her jaw, shaking her head like she was trying to clear water out of her ears.

"Can you still hear?" He asked gently, and Rose nodded quickly, letting him breathe out a sigh of relief. "You'll be fine for now then. I'll check you on the Tardis later."

He turned and cautiously opened the capsule door, stepping out slowly as he let his eyes seek out Lazarus. His body was splayed out across the floor, unmoving, but the Doctor hadn't expected to find the geneticist in his human form.

"I thought we were gonna go through the blender then," Martha gasped as she stepped out of the capsule behind him, and the Doctor forced himself to sniff in casual dismissal of the danger they'd all been in.

"It really shouldn't take that long just to reverse the polarity. I must be a bit out of practice," he offered casually, glancing over his shoulder at Rose as she stepped out at last, and rolled her eyes at him, pulling a grin onto his lips.

"Oh, shut up," she scolded lightly, and his grin softened to a smile before he turned and moved over to the still form of Lazarus.

"Oh god... He seems so human again," Martha admitted as she moved over to stand beside him. "It's kind of pitiful."

"Elliot saw that too," the Doctor said softly, turning his attention to Martha as Rose moved up to stand on her other side. "'This is the way the world ends. Not with a bang, but a whimper.'"

They stood in silence, just for a moment, before Rose moved. She stepped around Lazarus carefully and snatched up one of the large table cloths that had scattered about the room from knocked over furniture and fleeing guests.

She shook it out in silence and used it to cover the scientist's body, preserving some measure of modesty for the man who had hunted and killed indiscriminately, and his hearts swelled with affection.

She blinked and looked at him then, as though she'd felt his eyes on her, and Rose offered him a small smile before silently returning to his side and slipping her hand into his.

He tugged her into his side, and shook his head, "Come on, then. We'd best get outside. Don't want anyone asking too many questions, after all."

He urged the two women towards the stairs and into the night air, hoping to disappear into the crowds before police or ambulance services started questioning how they'd managed to stop the monster that Lazarus' experiment had turned him into.

From the moment that the Doctor had taken hold of Rose's hand beside Lazarus' body, he hadn't released it.

Not that she was complaining, Rose admitted to herself. Apart from the Tardis, nowhere felt more like home than his hand in hers.

As the three of them stood and watched an ambulance crew wheel Lazarus away in a body bag, she felt the Doctor's frame tense, and when she glanced up Rose could see him frowning after the geneticist.

He was blaming himself again, she recognised and stepped closer to him in response, her arm pressed against his and she squeezed his hand gently.

It was a soft, quiet reassurance, and she watched his lips lift just slightly as she redirected his attention from the death they hadn't been able to avoid to her presence beside him.

She could almost taste the questions that had begun to clamour behind his eyes, but he seemed to push them back, tilting his head in silent direction before turning to lead them all away from the authorities and their potential questions.

Martha moved with them, but Rose could see the young woman's eyes scanning the gathered groups of crying guests, seeking out her family.

As they walked, the Doctor let his free hand undo his bow-tie, and the top button of his shirt and Rose sighed softly.

"I'd have thought you'd know better than to wear that suit by now," she teased. "Every time you wear it, something goes wrong."

He shot her a look filled with a mixture of laughter and indignation, but before he had a chance to reply, Martha's family appeared, the two sisters embracing tightly and Rose grinned.

She let her eyes flick over Leo, before settling on Martha's mother and her smile vanished quickly.

The wide steps, the swing of her arms, the fire in her eyes. Rose knew that look. She'd seen that look directed at the Doctor before, and she also knew that he was as oblivious to the danger now as he had been the last time.

"Ah, Mrs Jones, we still haven't finished —"

Even as the Doctor attempted to continue a half-finished conversation that the woman probably didn't even remember, Rose let go of his hand and stepped forwards.

She lifted both hands in an attempt to soothe the woman's rage, but it appeared Mrs Jones didn't actually care who received her ire, as long as someone did, and Rose's head whipped to the side at the blow that landed across her cheek.

It took a moment for the pain to flare across her face, but when it did she drew in a hissed breath between clenched teeth, and the Doctor's long fingers wrapped around her upper arms as she swayed.

"You and that Doctor can stay the hell away from my daughter!" The woman was shouting at Rose, and she slowly lifted her head to level Martha's mum with a carefully neutral stare.

"Mum! What are you doing?!" Martha shouted but Rose wasn't concentrating on the family drama, her attention was on the stinging across her face and the cool hands on her arms.

"Rose?" She heard softly from behind her. His voice was carefully controlled fury and she let the Doctor turn her around and check her cheek, his eyes darkening at whatever he saw and Rose imagined her face was probably already bright red.

"How do you do it?" She asked, carefully keeping his attention, her question purposefully distracting him from the rising anger she could see in his eyes.

"Do what?" He asked her quietly, and Rose forced herself to smile despite the ache it brought to her face.

"Manage to annoy every mother you meet," she teased, and very slowly a smile curved over his mouth in response, his fury settling back down into a simmer.

"He is dangerous! I've been told things," Martha's mother was growling and Rose took a slow breath before turning to have her again, a frown creeping over her features.

"Told by who?" She asked, and Mrs Jones turned back to her in a flash.

"It doesn't matter who. Just look around! Death and destruction!" The woman snapped, and Rose felt her own temper flare.

"Actually, it does matter," she forced out, keeping her voice carefully calm. "I told you he's a genius, and this wouldn't be the first time his credibility has been attacked by a rival," she invented on the spot. If the look on Martha's face was anything to go by, her mothers' accusations were igniting her temper too.

"Besides, the Doctor didn't cause this! It was Lazarus' experiment that did the damage," Martha defended the Time Lord, "The Doctor saved us all!" she added, and even Leo backed them up, shooting his mother a look of strained patience.

"It was Tish who invited everyone to this thing in the first place, mum. If you need someone who's still alive to blame, I'd say, technically, it's her fault."

"Oh, thanks for that" Tish hissed, elbowing her brother in the side, but Rose could see the doubt beginning to grow behind Francine's eyes as her conviction wavered.

A sudden loud crash echoed around the area, and Rose turned towards the sound. The Doctor was already staring down the street and had taken two steps towards the chaos before he paused and glanced back at her and Martha, hesitating.

"Well, go on then," Rose prompted, "I'll catch up," she promised and with that, he took off at a run, Martha immediately moving to follow.

"Leave him," Francine pleaded, grabbing Martha's arm and pulling the young woman to a stop but the brunette shook her head, her eyes sad and full of disappointment with her mother, before she pulled free of Francine's grasp and chased after the Doctor.

"Martha?" Tish called, but her sister didn't wait, and Francine shook her head, tears welling up in her eyes when Tish dashed down the street after her sister.

"Not you too," she begged, and Tish hesitated, glancing back before wincing.

"Sorry," she offered, but she quickly dashed after Martha and Francine rounded on Rose.

"Stop. Right now," Rose hissed. "Whatever you were about to say, save it," she said, her voice harsh now that Martha wasn't there.

"I don't know who you've been talking to and right now I don't care," Rose told Francine, but her eyes flicked to Leo as well, including him in her words.

"You only need to know two things about the Doctor. The first thing is that there is no one on the entire planet who Martha is safer with. I can promise you that he would die for her. For Tish. For me. For you or your son. He hates wasted life, grieves over every death he witnesses, so no matter what Martha faces running after him, if he can, he will protect her," Rose said firmly, her tone brooking no argument from the woman before her.

"And the second thing?" Francine asked, voice cold but no longer full of open hostility.

"The second thing is that he never makes anyone come with him. In fact, he's been known to send people away if the situation becomes too dangerous. He stopped doing that with me when I kept getting into more trouble trying to get back to him than I would have been in just by staying with him," Rose offered the woman with a sad smile. "If Martha's running after him, it's because she wants to, and not because he talked her into it, or convinced her, or made her."

"And that's supposed to make me feel better, is it?" The woman snarled, and Rose shook her head, still smiling.

"No," she insisted, "it's supposed to make you recognise that no matter what you believe about how dangerous the Doctor's life is, it's your daughter's decision to follow him or not... and if she chooses to follow him, he will protect her with everything he has. That, in turn, should make you realise that whatever you've been told was said with malicious intent."

Rose paused, just long enough to watch Francine's eyes narrow in calculation, before she nodded, "If you'll excuse me," she finished, and moved away from the woman and her son.

Heading quickly down the street in the direction the Doctor had run, Rose hoped she'd catch up before the alien got into even more trouble.