Slamming the door to the rooftop closed behind them, the Doctor released Rose's hand just long enough to lock the door with the sonic, before he was rushing down the stairs, urging Rose and Martha ahead of him.
The three of them skid to a halt outside the lifts, Martha darting forward to press at the call button frantically, as the Doctor took hold of Rose's arm, eyes scanning over her quickly.
"Are you okay?"
"Looked like you were about to snog him," Martha accused, but the rebuke on the tip of his tongue was silenced by the humourless laugh Rose released.
"How else was I supposed to distract him?" She asked, glancing at Martha quickly before her gaze returned to his, "But yeah, I'm fine. What took you so long?"
It was part complaint, part familiar teasing, and he had the urge to pull her back into a hug.
"I haven't seen that Shaw woman—" Rose continued, falling silent when he released her arms and pulled back.
He tried to smother the grimace he knew his features were falling into but it was clear he'd failed when she breathed a soft "Ah... I take it you found her."
Martha stepped up to the lift again, mashing the button with impatience, and the lights began flickering violently, making her jump back, startled.
The sound of Lazarus throwing himself against the roof door echoed around them loudly, the screech of claws on metal making the Doctor's hair stand on end, and then the flickering lights failed completely, plunging them into a half light as an alarm began ringing around the building.
"What's happening?" Martha asked over the cacophony, and the Doctor winced at the noise assaulting his ears as Rose cursed.
"An intrusion triggers a security lockdown," she answered, "We're not going to be able to use the lifts, and the exits will be sealed. Everyone downstairs is trapped inside the building."
"He must be breaking through the door," the Doctor realised, running his hands through his hair as he tried to come up with a way to evacuate the guests and stop the monster coming for them.
"The stairs, now!" He snapped, the urgency in his voice propelling the two women toward the door of the nearest stairwell, "Come on!"
The loud bangs as Lazarus continued to tear his way into the building followed them, and the Doctor went first, leading the pair down the stairs quickly, knowing that the door would only hold so long.
A resounding crash ricocheted through the building, followed by several nightmarish growls and he heard one of the women stop running, throwing a glance over his shoulder just long enough to see Martha staring up at the top floor, her eyes wide with fear.
"He's inside!" She gasped, and Rose grabbed her elbow, forcing the young woman to keep stumbling down the stairs.
"Keep going, we haven't got much time!" The Doctor shouted back up at them both. Rose didn't even flinch, but his shout snapped Martha's head back around and she kept running.
He didn't wait for them, darting ahead by about half a flight of stairs he could still hear their steps behind him, and when he reached the bottom he dashed through the halls and into the demonstration hall again.
It was packed, and he ground his teeth in frustration. The intrusion alarm had been turned off, but it must have concerned someone. Surely, there was an evacuation procedure in place?
Rose and Martha both slid to a stop beside him only half a minute later, and he glanced sideways at the woman who always had the answers he needed as he realised she'd known exactly what the flickering lights and alarms had meant.
"You've seen the building plans?" He confirmed, and Rose nodded, her curls bouncing around her face as she brushed them back, her own agitation palpable.
"Is there another way out?" He asked.
"There's a fire escape in the back corner, but I'll need the sonic. Everything'll be locked down by now," Rose answered quickly, and he pulled the sonic from his pocket and tossed it to her without hesitation.
"You two, get everyone out," he ordered as she snatched it out of the air like they'd never been apart and he pushed back the grin that wanted to creep out from behind his panic.
"Setting fifty-four," he called as she spun away but Rose only turned back to him, walking backwards as she grinned.
"I remember!"
"Hurry!" He admonished, ignoring the warmth that flooded his chest at her words.
With Rose and Martha running for the secondary exit, weaving their way between small groups of gathered guests, the Doctor forced himself to focus on the danger to the hundreds of people crammed into the demonstration hall Lazarus Labs had set up.
A quick glance around the room, and he was moving towards the Professor's invention, using the podium to give himself some height so that he could gather everyone's attention and address the room.
"Listen to me!" He shouted, "You people are in serious danger! You need to evacuate out the side fire exit, right now!" The Doctor called, his voice drawing the eyes of the room.
"Don't be ridiculous," one of the women in the crowd called back and the Doctor's hands sank into his hair with barely restrained frustration.
"The most dangerous thing here, is choking on an olive," the woman scoffed, but before he could try again to convince these stupid humans to flee, the mutated form of the Professor finally caught up with them, crashing into the room by leaping from the mezzanine floor above the main hall.
He skid across the hard floor as he landed, limbs skittering out in an almost comedic manner and knocking over chairs and tables as he began to hunt.
Screams erupted around the room as the humans finally began to run, panic overwhelming them in a moment and they moved like a tide for the fire escape he'd ordered them towards only a minute before, but the Doctor watched in horror as many of the guests stumbled, fell, scattered, and were left to the mercy of Lazarus.
The creature spun on the woman who had been arguing with the Doctor only moments before, her fear-numbed fingers dropping her champagne glass as she stared in frozen terror at Lazarus.
"No! Get away from her!" The Doctor shouted, but he was too slow. Lazarus' new tail reared over like a scorpion, impaling the woman as her scream rent the air.
Before the Doctor had time to consider and discard more than half a dozen plans to save her, the woman's body dropped to the ground, looking exactly like the corpse they'd found of Sylvia Shaw.
'It happened so fast,' the Doctor thought as he stared at the body, sucking in deep breaths of mixed fury and revulsion at the wasted life before him, refusing to look too closely at the unravelling timelines.
Lazarus turned slowly, his legs sliding against the slippery floor as he stalked towards another victim, and the Doctor snarled when he realised it was Martha's family.
"Leave them alone, Lazarus!" He shouted over the screams and cries of abject fear still echoing through the hall from the direction of the fire escape, taking half a step across the podium towards the mutation and drawing the Professor's attention away from the Jones'.
When Lazarus paused and spun back to face him, the Doctor felt his frame rear back as his own panic grasped his throat. Rose would never forgive him if he had to regenerate now.
Behind Lazarus, he could see Mrs Jones cradling her son's head, and a moment later Martha had slid to her knees beside them. He met her terrified eyes and quickly formulated a new plan. He had to get Lazarus out of the room, away from the guests and his potential victims.
Away from the people under his protection. To give Martha a chance at getting her family out alive.
And if Martha was here, it was only a matter of time before Rose was back within striking distance too.
"What's the point?" He snarled, keeping Lazarus' attention on him as Martha began to treat her brothers' head wound.
"You can't control it! The mutation's too strong!" The Doctor taunted, his eyes flicking around the room as he sought some kind of plan. He forced himself to stand his ground as Lazarus slowly approached him, one ground-shaking step at a time, and swallowed back his nerves as he let his gob keep talking.
"Killing those people won't help you. You're a fool. A vain old man who thought he could defy nature. Only, nature got her own back, didn't she?" The Doctor sneered, hearts pounding as he purposefully attacked Lazarus' pride, intentionally infuriating the creature.
He could see the building rage in Lazarus' face, could taste it on the air above the scent of human fear, but he couldn't risk the geneticist aiming his attention at Martha, her family... Or Rose.
"You're a joke, Lazarus! A footnote in the history of failure!"
The creature reared back, furious, and its tail reared up high once more, ready to strike and aimed directly for the Doctor.
"Oh, well, that did it," he muttered to himself before turning and running.
He slid around the first corner he found, dashing into a corridor lined with labs, but he could hear Lazarus following close behind.
A quick glance over his shoulder showed that instead of crashing into the wall as he careened around the tight corner, as the Doctor had hoped, the geneticist had skittered up the wall and was now running along the ceiling like some kind of spider.
The Doctor knew he had to get ahead of Lazarus if he had any hope of surviving, so he pushed on faster. Briefly, he wished that he'd spared a minute or two to look at the building layout as Rose had, but he brushed the thought aside.
Life wouldn't be nearly as interesting if he planned ahead, he admitted to himself. Pushing forth another burst of speed, the Doctor made two or three more sharp corners, before he rashed through a door that seemed to lead into what looked like the central backbone of the building.
Electrical conduits, water pipes, gas tanks, and various other pipes and panels for the building's structural integrity and its utilities filled the large room, and the Doctor slowed just enough to keep his footsteps silent as he moved through them all.
As he climbed up maintenance ladders and crept between huge pipes looking for another exit, he heard the door he'd come through slowly creak open. The ominous skittering of Professor Lazars's new limbs reached his ears, and he crept through the room as quickly as he could, hoping for a way out before he was inevitably discovered.
"It's no good, Doctor," Lazarus' voice rumbled through the room, its direction hidden by the hissing pipes and crackling buzz of old lightbulbs "you can't stop me."
"Is that the same arrogance you had when you swore nothing had gone wrong with your device?" The Doctor called, pausing his movements as he strained his hearing, trying to figure out where Lazarus was. The last thing he wanted to do was run headfirst into him.
"The arrogance is yours," Lazarus replied, growling, and the Doctor kept moving again, making sure that even as he tried to track the scientists' location via his voice, the same couldn't be done in reverse.
"You can't stand in the way of progress!" Lazarus cried out, his words a clear taunt but the Doctor couldn't help but respond.
"You call feeding on innocent people progress? You're delusional!" The Doctor snarled, but Lazarus just laughed.
"It is a necessary sacrifice," the monster declared, and the Doctor felt his resolve harden, even as he spotted the giant mutant and ducked quickly to avoid being seen.
"That's not your decision to make."
He crept away from Lazarus' current location, but it seemed like their conversation was officially over as the scientist didn't deign to argue his viewpoint further.
Suddenly, the main power was restored and the Doctor glanced up at the now bright lights automatically, before freezing in horror at the sight of Lazarus hanging over him like some kind of malevolent spider.
"Peek-a-boo!" The smug creature sang, and the Doctor swallowed hard.
"Oh," he muttered, eyes wide as Lazarus hissed, his tail flicking, "hello..."
Lazarus' chin split in half, opening his mouth into a gaping maw full of teeth and the Doctor launched away springing into a run straight for an exit he'd seen on the far side of the room without looking back.
Caution no longer a priority, the Doctor clambered around pipes and railings as he frantically moved out of Lazarus' reach, pushing into the maintenance corridor past the door and bouncing off walls as he fled once more into the main laboratory, eyes seeking anything he could use to halt the mutation still chasing after him.
Martha had done her best to keep the panicking crowds back from Rose as she ran the sonic over the locked fire escape, but the moment the doors parted the guests started leaving like a flood of bodies, pushing her along with them.
It was only the blonde's tight grip on her arm, her other hand clinging to the doorframe, that stopped both of them from getting knocked aside in the crush.
"Martha, go get your family!" Rose shouted at her over the fear-filled shouts and incoherent screams of the guests.
Martha didn't need to be told twice, and nodded her thanks at the other woman, before fighting against the flow of people to get back into the main room.
She arrived back just in time to see Lazarus drop another corpse to the ground with a loud thud, and turn on her mum and brother. Both of them were on the ground, staring up at the monster looming over them threateningly with horror on their faces, but the Doctor drew Lazarus' attention.
"Leave them alone Lazarus!" The Doctor shouted, and Martha took her opportunity, dashing across the room.
As she ran, Martha let herself drop to her knees, her momentum, her silky dress, and the hard floor let her slide across the final distance until she was beside her mum and Leo, and her training kicked in quickly when she spotted blood coming from her brother's head.
Martha glanced at the Doctor, and his eyes met hers. For just a moment, she saw his jaw tense and determination fill his gaze before he shifted his attention back to Lazarus and she knew he was going to do something stupid.
Just like when he'd offered himself up to the Daleks.
As the Doctor continued shouting at the scientist, keeping the creature's attention, Martha spun on her knees and grabbed up a clean napkin, scooping ice from an overturned ice bucket, and prepared a makeshift compress for her brother's head.
Tish appeared at her elbow, and even though all of them were still in danger, something in Martha's stomach uncoiled to know that all her family was still alive and right there beside her.
"What's he doing?" She heard Tish hiss
"He's trying to buy us some time," Martha whispered back quickly, not wanting to tip off Lazarus, "so let's not waste it."
She turned back to Leo and she handed the ice pack to her mum to hold it against her brother's head.
"Leo, look at me," she said softly, drawing his attention quietly without grabbing Lazarus', the Doctor still shouting taunts behind her. "Focus on me. Let's see your eyes," she prompted, noting a difference in their dilation and grimacing.
"He's got a concussion. Mum, you'll need to help him downstairs," she hissed. "Try and keep the ice on his head, that'll keep the swelling down."
"You're a joke, Lazarus! A footnote in the history of failure!" She heard the Doctor shout. Lazarus roared with inarticulate fury, and Martha flinched, hands rising to her ears as she turned around and stared as the Doctor fled the room, and Lazarus quickly gave chase.
"Come one, move!" She ordered her family, "Let's go, we need to get out of here!"
She ushered her mum and Leo ahead of her, keeping Tish at her side with a hand on her sister's arm, and urged them all forward until the fire escape was in their sights again, Rose still standing there and directing any stragglers escaping the main hall.
"You all right?" Rose called the moment she spotted Martha, and Martha couldn't help feel a warm rush of gratitude that Rose had sent her back in after her family.
"Leo's got a concussion, but he'll be okay. The Doctor–"
"He's being bait, if I know him," Rose growled as they finally limped up to her side, and she began walking with them.
They moved through a second pair of doors, and down another flight of stairs before finding all the guests pressed against a final set of doors that led to the outside. Based on the clamouring and panic, this final obstacle to their escape was still sealed, and Rose cursed beside her.
"Damn it, these weren't in the plans," the blonde hissed sharply, and Martha began to look around the foyer while her sister started to panic, shock finally setting in.
"Oh my god, we're trapped!"
"There must be an override switch somewhere. Tish, where's the security desk?" Martha demanded. Her sister worked for the labs, she was head of PR, she had to know where the security desk was located, and Martha grabbed her sisters' arms, shaking her gently to get her to focus.
"Umm... Over there...!" Tish spluttered, pointing at what looked like a solid wall, but two steps towards where her sister was pointing, and Martha realised it had been an optical illusion, hiding the security station.
Rose pressed the sonic screwdriver into her hand, and Martha blinked at her in surprise, but the blonde just smiled.
"It's already on setting fifty-four," she explained, "get everyone out of here."
Without waiting for Martha to reply, the woman grabbed her long skirt in her hands and began running back up the stairs and into the labs as Martha gaped after her.
"Stupid woman! She'll get herself killed!" Her mum's snarl snapped Martha out of her own surprise, and she flung a glare at her.
"Maybe, but she's trying to help and that's more than I can say for everyone else standing here, panicking!" Martha snapped at her mother before she tightened her grip on the precious sonic screwdriver and dashed for the security desk.
She pushed her anger at her mum to the back of her mind as she darted around the false wall and moved back until she found a wall of switches.
She let her eyes scan over the controls for a second, but none of it made any sense to her, so she backed up a couple of steps and aimed the sonic at the largest circuit board, hoped that the alien tool would be able to figure out the rest, and pressed the button.
It buzzed in her hand, giving out the same soft reassuring hum that it always did, and seconds later the emergency lighting shut off as the main power was restored to the building.
Once the lockdown was lifted, the external doors released and slid open, and the panicked crowds quickly began pouring out onto the street as Martha let loose a wordless shout of relieved success.
She quickly came out from behind the security desk, but one look at her family and she braced herself for a fight. They were standing inside the now open doors, waiting for her, and she was about to let them down.
"I've got to go back in," she said gently, and her mum's jaw dropped as fear flooded her face. "I've got to see if I can help them."
"You can't! You saw what that thing did, it'll kill you!" Her mum cried, and Martha pressed her lips together to silence her own fears and shook her head.
"Maybe. But I have to try," she explained, and her mum's fear gave way to a cold anger.
"It's that Doctor, isn't it? That's what happened to you. That's why you've changed," she spat venomously, stepping forward to grab hold of Martha's hands in a near-vicelike grip.
It hurt, but her mum's words hurt more and she pulled her hands away and took a step back, tears choking her.
"I want to be a doctor so that I can help people, mum. If I run away right now how is that helping anyone?" Martha asked, and she could see her mum clenching her teeth as she struggled to find an answer.
"He was buying us time, Martha. That's what you said," Tish tried to convince her. "That was time for you to get out too... and there's people out here you can help."
Martha let her eyes slide from Tish to Leo, waiting for him to join in too, but instead he just offered her a nod of silent support and she smiled, her back straightening with determination.
"There's no one out there I can help more than the ambulances already on their way can. And I'm not leaving him or Ro— Or Mal Lupin in there alone. I want to help them," she said firmly, taking another step away from her mum and turning to head back into the labs.
Her mum was calling after her, shouting her name, but Martha forced herself to ignore the fear-fueled tears she could hear in her mum's voice. It took a lot to walk away from her family, but Martha knew there would be paramedics on the scene soon, and probably police as the panic-stricken guests called frantically for help.
She was still a medical student. She knew there was nothing she could help with outside that wasn't already being seen to, but she could help the Doctor and Rose stop Lazarus from hurting anyone else.
'Assuming', she thought to herself, 'that I can find either one of them.'