A/N: Welcome back! Get ready for a new chapter update. This takes place during the Doctor Who episode 'The Lazarus Experiment'.

I do not own Doctor Who. All I own is this story, and my OC Katy.

Please review and no flaming will be tolerated. Thanks 😊

VANITY IN SCIENCE

"Feed yourself with my life's work. How many likes is my life worth?"
 – The Chainsmokers: 'Sick Boy' (Sick Boy [2018])

Tardis

The time had come to drop off Martha back to her home. The Doctor had done what he had promised he would do to repay Martha for helping them out at the hospital. Katy and Martha clung to the side of the console as the Doctor landed the Tardis as gently as he could without jostling them too much and put on the handbrake.

"There we go. Perfect landing. Which isn't easy in such a tight spot," the Doctor stated brightly.

"You should be used to tight spots by now," Martha teased back. "Where are we?" She wondered curiously, missing the sympathetic, pitying expression on Katy's face.

"The end of the line. No place like it," the Doctor responded, and Katy winced. Martha eagerly heads for the double doors, excited for what she was about to discover outside …

Martha's Flat

… and found herself standing in the middle of her living room in her London flat. Her expression dropped in disappointment. Now that her time was up, Katy knew it was going to be hard for Martha to accept the fact that she had to return to normal life after being shown the wonders of the universe. Martha turns and looks at the Doctor with sad eyes, as he and Katy both stepped from the Tardis so they could make their final farewells.

"Home? You took me home?" Martha accused as the Doctor nodded, nonchalantly.

"In fact, the morning after we left, so you've only been gone about twelve hours. No time at all, really." The Doctor stated, and Katy smirked at him.

"Your timing has improved, love." She observed, elbowing him in the side, and earning a quizzical look from him. "At least it's not twelve months like last time."

"Ugh, you're never gonna let me live that down, are you? It was just that one time…" the Doctor retorted, whining a little. "And at least there's no mothers around to slap me." He noted as he absently rubbed the side of his face to soothe a long forgotten phantom pain.

"You did kinda deserve that though; you scared the hell out of Mum—"

"—But all the stuff we've done," Martha interrupted the slightly confusing conversation she was overhearing between them and returned the focus to the situation at hand. The Doctor and Katy flushed a little, remembering Martha was still there. "Shakespeare, New New York, old New York?" She reminded them, and the Doctor nodded.

"Yep, all in one night, relatively speaking. Everything should be just as it was." He wonders around the room, inspecting things curiously. "Books, CD's, laundry…" The Doctor slyly snags a pair of Martha's knickers from a nearby clothes horse with his fingers and holds them up for Martha to see. She flushes red and snatches them from him.

"Doctor! Honestly…" Katy chides him, unamused.

He clears his throat, looking sheepish.

"So, back where you were, as promised."

"This is it?" Martha stated.

"Yeah, we should probably, er—" the Doctor is abruptly cut off when Martha's phone rings and the answering machine picks up. All three of them stare down at the machine.

"Hi, I'm out. Leave a message!" Martha's recorded voice speaks up.

"I'm sorry," Martha winces as the Doctor and Katy gestured dismissively.

"Martha, are you there? Pick it up, will you?" An older woman's voice requests, rather imperiously.

"It's Mum. It'll wait." Martha reassures them. Francine, Martha's mother, sighs impatiently.

"All right then, pretend that you're out if you like. I was only calling to say that your sister's on TV. On the news of all things. Just thought you might be interested."

Francine hangs up, and Martha immediately turns to grab her remote and switches on the TV, which was on stand-by. Immediately, they see an image of Tish, Martha's sister, standing next to an elderly man who is in the middle of making an announcement.

"The details are top secret…" the elderly man stated, looking somewhat arrogant.

Martha frowns.

"How could Tish end up on the news?"

"Tonight, I will demonstrate a device which will redefine our world…" the man continues.

"Looks like your sister's got a job…" Katy observed, curiously.

"Yeah, PR for some research lab." Martha confirms.

"… with the push of a single button, I will change what it means to be human!" The man brags, and Martha immediately puts the TV back on stand-by and turns back towards the Doctor and Katy.

"Sorry," She apologises once again. "You were saying we should…?" Martha prompted and the Doctor refocuses.

"Yes, yes, we should." He agrees, gesturing between himself and Katy; much to Martha's disappointment. "One trip is what we said."

"Yeah. I suppose things just kind of escalated." Martha realises and the Doctor grinned, once again looking a bit sheepish.

"Yeah. Seems to happen to me a lot."

"Tell me about it…" Katy muttered underneath her breath, and playfully pokes her tongue out at the Doctor when he gives her a playful glare for the comment. Martha smiles weakly at their banter.

"Thank you. For everything." Martha tells them both, and steps forward to pull Katy into a friendly hug, which the brunette reciprocated warmly.

"We had a lot of fun … for the most part." Katy stated and Martha giggles at the comment a little.

"It was my pleasure," the Doctor grinned at her. They both go back into the Tardis, and Martha sadly watches as it dematerialises. She sighs and turns away to get on with her day but pauses when the Tardis unexpectedly materialises back again. The Doctor reopens the double doors and sticks his head out, frowning at Martha in bewilderment. "No, I'm sorry. Did he say he was going to change what it means to be human?"

"Yeah, I believe that's exactly what he said." Katy confirms what he said from inside the confines of the Tardis. Her comment earned an amused look from Martha and a flat look from the Doctor.

"What's the big deal?" Martha prompts, looking quizzically at the Doctor, who looked a little bit concerned about what the elderly man had just said on the TV.

"The big deal is, the idea to change what it means to be human, should be impossible." The Doctor reiterated, seriously. "This warrants some further investigation." He decides and Martha brightens a little, pleased that her friends weren't leaving just yet. Perhaps she could figure out a way to convince the Doctor to extend her traveler's privileges on the Tardis.

Katy sidles up to the Doctor and smiles at him.

"Of course it does. But you do realise that it could all be a misunderstanding, and you're probably making a mountain out of a molehill over something potentially harmless?" Katy points out, and the Doctor shrugged.

"Probably. But I'd rather make sure. That technology in the wrong hands could spell disaster."

"So, we're crashing a party?" Martha prompted.

"Looks like it, yeah." Katy confirmed and sighed heavily. "I'll go look for something to wear in the wardrobe…" She stated, before looking at Martha for confirmation. "What's the dress code?"

"Uh, if it's a PR party, probably formal." Martha stated.

Street

The Doctor, Katy, and Martha stroll down the street dressed in formal evening attire. The Doctor looked incredibly uncomfortable in his tuxedo, as he fussed with his black bow tie looking somewhat agitated.

"Oh, black tie. Whenever I wear this, something bad always happens." He bemoans, and Katy raises an eyebrow at him, curiously.

"When was the last time you wore that?"

"Uh, in Pete's World. During Jackie's birthday party. Rose and I were playing the part of the serving staff," the Doctor recalled, and shuddered at the memory. Katy paled a little, remembering the Cybermen that had literally crashed the party and killed partygoers and wait staff. Including Jackie Tyler.

"Oh, yeah. Say no more…" Katy agreed, smoothing down her dress to remove any wrinkles.

The brunette had managed to find a lovely white evening dress in the Tardis's immense wardrobe. It was a halter-neck, sleeveless and had a slit that ended halfway up her thigh for easy leg room. In fact, the Doctor had flushed a little and was speechless when he had seen what she was wearing, and looked a bit flustered, much to the brunette's amusement.

"It's not the outfit, that's just you." Martha pointed out, fixing a stray hair that had fallen out of place from her hairband. "Anyway, I think it suits you." She complements him, and Katy grinned in agreement.

"It does?" the Doctor was surprised.

"Absolutely. In a James Bond kind of way," Katy added.

The Doctor scoffed at the very idea.

"James Bond?" Then mentally pictures the fictional British Spy and has a change of heart at the idea. "Really?" He preens himself, and both Katy and Martha giggle at him, causing the Doctor to flush bashfully. They walk up to a building labelled Lazarus Laboratories and breeze on inside the building.

Reception Room

In the middle of the room is a circular dais. On it is a man-sized frosted glass chamber and four upright posts, slightly curved at the top to aim at the chamber. As the trio stop to admire the piece of machinery, a waiter walks by, holding a tray of food aloft in his hand. The Doctor instantly beams with delight when he sees the hors d'oeuvres.

"Ooh, look, they've got nibbles!" He reaches for a handful. "I love nibbles!" The Doctor stuffs a couple into his mouth, causing Katy and Martha to wince a little.

"So we noticed," Katy commented, reaching for a glass of champagne from yet another passing waiter and took a dainty sip from it, just to keep her hands busy. Tish spots Martha and approaches them carrying a clipboard and wearing a Bluetooth device in her ear, looking warmly at her sister as she greets her.

"Hello!"

"Tish!" Martha grinned at her sister and hugs her. Katy and the Doctor observe this with pleasant smiles on their faces. Tish eye sweeps Martha from head to toe and smiles approvingly.

"You look great. So, what do you think?" She gestures around the reception area, looking at her sister expectantly. "Impressive, isn't it?"

"Very," Martha compliments, politely.

"And two nights out in a row for you. That's dangerously close to a social life," Tish teases and Martha gives an exaggerated sigh.

"If I keep this up, I'll end up in all the gossip columns." She plays along with the light-hearted joke.

But Tish gives her a very serious look.

"You might, actually. You should keep an eye out for photographers," She warns, then falters a little, looking a bit weary. "And Mum, she's coming too. Even dragging Leo along with her."

"Leo in black tie?" Martha looked surprised. "That I must see." Katy clears her throat, hinting for Martha to introduce her and the Doctor to Tish. "Oh! This is, er, the Doctor. And Katy." She gestures towards the Doctor and Katy who smile politely at Tish, who doesn't smile back, but instead frowns at them, curiously.

"Are they with you?" She asks Martha.

"Yeah," Martha confirms. Tish consults her list on the clipboard, flicking through the various pages attached to it.

"But they're not on the list. How did they get in?" Tish demanded, sharply.

Martha looks a little bit embarrassed.

"They're my plus two…" She explained.

"So, this Lazarus," the Doctor neatly steps in to sidestep the explanation about how he and Katy managed to get a guernsey into the PR party. "He's your boss?" He questioned casually.

" Professor Lazarus, yes." Tish corrects the Doctor, earning a discrete roll of the eyes from Katy. "I'm part of his executive staff."

"She's in the PR department," Martha clarifies.

"I'm head of the PR department, actually." Tish once again corrects, and Martha looks at her sister in surprise.

"You're joking."

"I put this whole thing together," Tish explained, somewhat smugly. Katy is caught between looking impressed and mildly irritated at the mildly defensive tone she could sense in Tish's words, as the Doctor nodded politely at the little piece of information he had just received.

"So do you know what the professor's going to be doing tonight?" He inquires, getting to the whole point of them gatecrashing an exclusive PR party. He points towards the frosted glass chamber casually. "That looks like it might be a sonic microfield manipulator." The Doctor observed.

"He's a science geek," Tish scoffs and the Doctor blinks at her in confusion, while Martha looked pained and Katy a bit territorial. "I should have known. Got to get back to work now. I'll catch up with you later." Tish walks off, and the Doctor looks at Martha for an explanation.

"Science geek? What does that mean?"

"That you're obsessively enthusiastic about it, sweetie." Katy explains to him, wrapping a hand around the Doctor's bicep, as Martha nodded in confirmation. The Doctor immediately looks chuffed.

"Oh, nice!" he grins happily.

Katy giggles at him, before spotting a familiar person entering from the opposite side of the room, holding both onto a champagne glass and onto the arm of a young man wearing black tie, with similar features to Martha.

"Hey, Martha? Isn't that your Mum over there?" Katy points towards Francine and Leo, Martha's younger brother. Martha turns her head in the direction Katy was pointing at and beams happily when she sees her mother. Francine likewise smiles warmly when she sees her daughter.

Martha," She greets her.

"Mum!" Martha immediately gives her mother a big hug. Francine reciprocates the hug, looking a bit bemused by her daughter's reaction.

"Alright, what's the occasion?" She inquires, curiously.

"What do you mean? I'm just pleased to see you, that's all." Martha responded, surprised by her mother's reaction.

"You saw me last night," Francine points out.

"I know. I just miss you," Martha admitted truthfully before turning towards Leo, who was studying her with both amusement and curiosity. "You're looking good, Leo."

"Yeah," Leo shrugged nonchalantly. "But if anyone asks me to fetch them a drink, I'll swing for them." He joked, earning a giggle from Katy; whom he winked at, much to the Doctor's annoyance.

Francine raised an eyebrow at her daughter.

"You disappeared last night." She noted, and Martha shrugged, making an attempt not to look sheepish as she responded to her mother's observation.

"I just went home," She confirmed.

"On your own?" Francine frowned disapprovingly at Martha, who chooses to change the subject and introduce her friends to her family.

"These are friends of mine. Katy Tyler, and the Doctor." She gestures to both of them and Katy smiles politely at the older woman.

"Pleasure to meet you, ma'am." Katy acknowledges and earns a curt nod from Francine who focuses curiously on the Doctor.

"Doctor what?"

"Just the Doctor," Martha clarifies. "We've been doing some work together." Francine looks suspiciously at the Doctor as Leo takes things in his stride and leans in to offer the Doctor his hand in a friendly greeting.

"You all right, mate?" He questioned the Doctor's wellbeing, and the Time Lord merely nodded in agreement before turning his attention back on to Francine, looking a little nervous; considering that yet again he was meeting another one of his companions' mother. He just hoped that she wasn't slap-happy like Jackie had been.

"It's lovely to meet you, Mrs Jones. Heard a lot about you," the Doctor said cheerfully and Francine raises an eyebrow at his response.

"Have you? What have you heard then?" She asks, and the cheerful smile on the Doctor's face falls a little, obviously realising that he had cornered himself unintentionally and now had to scramble for an appropriate answer to appease this already highly suspicious woman.

"Oh, you know, that you're Martha's mother, and…" he trails off and Katy wades in to hopefully aid her boyfriend from an increasingly hopeless situation concocted by Martha's mother.

"…and how much she loves you. Honestly, we've never heard someone brag as much as Martha does about you. Makes me miss my own mother so much." Katy stated as cheerfully as she could without making it obvious that her response was completely improvised.

She jumps a little then relaxes and squeezes back when she feels the Doctor reach out and grab her hand, interlocking their fingers together. He leans in, kisses her temple, and mumbles into her ear.

"Thank you, love." He sounded both grateful and relieved for Katy's quick thinking.

However, they both could see that Francine still didn't look entirely convinced with Katy's answer and continued looking at them both calculatingly, while Martha just looks embarrassed by her mother's interrogation and winces apologetically at her friends. Someone tapping on their glass draws their attention and they turn to see Professor Lazarus attempting to gain everyone's attention.

"Ladies and gentlemen, I am Professor Richard Lazarus and tonight I am going to perform a miracle. It is, I believe, the most important advance since Rutherford split the atom, the biggest leap since Armstrong stood on the moon. Tonight, you will watch and wonder. Tomorrow, you will wake to a world which will be changed forever." Lazarus hands the microphone to an assistant, before shuffling his way into his chamber.

A couple of lady scientists start up the machine and press a big button. The four columns start to oscillate and rotate around the chamber as they pour energy into it. The entire time, the Doctor had a stony expression on his face. He did not like the look of what was happening in front of him. Then an alarm sounds, making the Doctor jump into action.

"Something's wrong. It's overloading!" He shouts anxiously. Everyone flinches when the computer suddenly starts sparking from the controls and smoking. The Doctor immediately drops Katy's hand and rushes over, vaulting the counter and getting out his sonic screwdriver as he opened up the machine and started sifting through the wires.

"Somebody stop him. Get him away from those controls!" A nearby elegantly dressed older woman, roughly the same age as Lazarus, yells out in protest. Katy darted closer and gets in her face, somewhat impatient.

"If that thing goes up, it might take the whole building with it. Is that what you want?" She points out, earning a look of disdain from the woman who sniffs at her haughtily. Katy ignores this in favour of focusing on her boyfriend who had managed to pull out a big power cable. He disconnects it from the contraption, which gradually slows down, then stops. Katy, who was closer than Martha was to the machine, rushes over to the chamber.

"Get it open!" the Doctor shouts, and Katy pulls open the door, releasing plumes of white smoke from within.

Slowly a young man staggers out, causing both the Doctor and Katy to look at him with shock. The older woman who protested earlier, beams with delight at the sight of him. Lazarus looked a bit dazed at first, but slowly raises his smooth, youthful hands to his equally youthful face and touches it experimentally. A huge, triumphant smile spreads across it.

"Ladies and gentlemen, I am Richard Lazarus. I am seventy-six years old, and I am reborn!" He announces loudly to wild applause from everyone except for the Doctor, Katy, and Martha who look very disturbed.

"He did it. He actually did it!" the haughty older woman gushes, with excitement.

A while later, Lazarus poses for some photographers who had come along to the event to document everything, with the older woman clutching his arm and beaming from ear to ear in front of the cameras also. The Doctor, Katy, and Martha had regrouped not too far away, and were deep in discussion with what they had just observed.

"I doff my hat to you, sweetie. You made the right call about us attending this party." Katy praised the Doctor, looking at Lazarus with a look of deep revulsion. "That can't be normal…"

"It can't be the same guy," Martha agreed with Katy. "It's impossible. It must be a trick."

"Oh, it's not a trick," the Doctor unfortunately confirms their worst fears. "I wish it were."

"What just happened then?" Martha questioned.

"He just changed what it means to be human," the Doctor was grim.

"And it just might have grave consequences." Katy hypothesised as the three of them move closer to confront Lazarus on his 'achievement'. They overhear the older woman, whom they learned was called Lady Thaw, fawning over Lazarus.

"That was the most astonishing thing I've ever seen. Look at you!" She indicates to his new appearance, and Katy could see the dollar signs popping up in this woman's eyes, much to her disgust.

Lazarus smirked very pompously.

"This is only the beginning. We're not just making history, we're shaping the future, too."

"Think of the money we'll make. People will sell their souls to be transformed like that." Lady Thaw stated. "And I'll be first in line."

Suddenly, Lazarus stiffens like he had been prodded with a cattle prod, and gasps, before snatching a nearby serving tray from a passing waiter and proceeds to stuff all the hors d'oeuvres in his mouth, alarming Lady Thaw.

"Richard…" Lady Thaw looked appalled at his rudeness, but he merely shrugged it off dismissively.

"What? I'm famished." Lazarus stated defensively and continued eating. The trio sidle up to the couple, allowing the Doctor to put forward his two cents.

"Energy deficit," both Lazarus and Lady Thaw look at him in surprise. "Always happens with this kind of process." The Doctor states, casually. Lazarus raises an eyebrow at the Doctor's observation with interest.

"You speak as if you see this every day, Mister…?"

"Doctor," the Doctor responded. "And well, no, not every day, but I have some experience of this kind of transformation."

"That's not possible," Lazarus scoffs. The Doctor's eyes twinkled and he moves in for the metaphorical kill to prove he knew exactly what he was talking about.

"Using hypersonic sound waves to create a state of resonance," Lazarus's eyes widen in astonishment, while Lady Thaw just glares at him for outsmarting her husband. "That's inspired."

"You understand the theory, then." Lazarus commented.

"Enough to know that you couldn't possibly have allowed for all the variables," the Doctor responded.

"No experiment is entirely without risk," Lazarus countered and the Doctor just looks at him flatly.

"That thing nearly exploded. You might as well have stepped into a blender."

"You're not qualified to comment," Lady Thaw snipes at him.

"And you are?" Katy retorted, ignoring the look of lewd interest that Lazarus gave her, which made her stomach flip over unpleasantly and she stepped closer to the Doctor, who wrapped a protective arm around her waist. He too had seen the look Lazarus had given Katy and was none too pleased to see it either.

"If I hadn't stopped it, it would have exploded," the Doctor carried on as though Lady Thaw had not even spoken. Lazarus looked like he wanted to argue with this strange young man and his opinion, but instead chose to 'graciously' thank him for his assistance.

"Then I thank you, Doctor. But that's a simple engineering issue. What happened inside the capsule was exactly what was supposed to happen. No more, no less."

"You've no way of knowing that until you've run proper tests," Martha pipes up.

"Look at me," Lazarus insisted, sounding a bit exasperated with the negative feedback he was receiving. "You can see what happened. I'm all the proof you need."

"This device will be properly certified before we start to operate commercially," Lady Thaw reassures them.

Both Katy and Martha look at her with horror.

"Commercially?" Katy blurted out.

"You're joking. That'll cause chaos!" Martha protested. The Doctor frowned disapprovingly at them for their obvious foolishness.

"This isn't about improving. This is about you and your customers living a little longer."

"Not a little longer, Doctor. A lot longer. Perhaps indefinitely." Lazarus smirked.

"Richard, we have things to discuss, upstairs…" Lady Thaw indicated to some nearby stairs, and Lazarus nodded, handing off the serving tray to yet another passing waiter. He takes Lady Thaw's arm.

"Goodbye, Doctor." Lazarus states to the Doctor, insincerely. "In a few years, you'll look back and laugh at how wrong you were." He then looks at Katy and reached for her hand to plant a kiss on the back of it. Katy wrinkles her nose in revulsion as Lazarus gives her a lusty wink before leaving with Lady Thaw.

"Oh, he's out of his depth. No idea of the damage he might have done," the Doctor stated the moment Lazarus and Lady Thaw were out of hearing range.

"So what do we do now?" Martha asks him, looking slightly worried.

"Now? Well, this building must be full of laboratories. I say we do our own tests," the Doctor suggested, and Katy grinned at the both of them and raises her hand up to show them.

"Lucky I've collected a DNA sample, huh?" She stated, and the Doctor grinned at her proudly.

"Oh, Katy Tyler, you're a star!" He praises his girlfriend before the trio make a beeline towards one of the nearby laboratories.

Laboratory

The Doctor takes a swab and wipes it over the back of Katy's hand where Lazarus had kissed it, before re-distributing it onto a microscope slide, and he and Martha examine it while Katy goes and washes her hands. When she returns, the Doctor and Martha were still pouring over an image of a strand of DNA projected on a computer screen. The Doctor was grinning from ear to ear at what he was seeing.

"Amazing," He grinned.

"What is?" Martha asked, as Katy sidles up beside the Doctor and peers curiously at the screen.

"Lazarus's DNA." The Doctor explained, and Martha frowns curiously at the screen.

"I can't see anything different," She states.

"Look at it," the Doctor insists, and both girls gasp in shock and awe when a split second blip occurs on screen that indicated something strange had happened to the DNA strand.

"Oh, my God. Did that just change?" Katy questioned with wide eyes. "But it can't have."

"But it did," the Doctor confirmed.

"That's impossible," Martha shakes her head disbelievingly. The Doctor turns away from the computer monitor and addresses both girls.

"And that's two impossible things we've see so far tonight," He grinned enthusiastically. "Don't you love it when that happens?"

"Only if nothing dangerous comes of it…" Katy agreed, a little pessimistic.

"That means Lazarus has changed his own molecular patterns." Martha realises with alarm.

"Hypersonic sound waves to destabilise the cell structure, then a metagenic programme to manipulate the coding in the protein strands." Both girls looked confused; especially Martha, who was likely to have studied this as part of her medical studies. The Doctor attempts to explain. "Basically, he hacked into his own genes and instructed them to rejuvenate."

"But they're still mutating now," Martha points out.

"Because he missed something. Something in his DNA has been activated and won't let him stabilise. Something that's trying to change him." The Doctor stated, grimly.

"Change him into what?" Katy asked.

"I don't know, but I think we need to find out." The Doctor decided, and both girls nodded.

"That woman said they were going upstairs," Katy reminded them and the Doctor nodded and takes her hand, heading in that direction.

"Let's go," he tells both girls who nodded and followed him out.

Lazarus's Office

Lazarus's office was like an aircraft hangar; enormous with lots of empty spaces, filled up with meagre pieces of furniture, and large windows that allowed a view of the entirety of London. A place that screamed of wealth and extravagance. Or at least that was Katy's first opinion when she, the Doctor, and Martha stepped through the double doors of the lift and right into the office.

"This is his office, all right." Martha observes.

"So where is he?" the Doctor questioned, somewhat impatiently.

Katy and Martha glance around to see if they could spot either Lazarus or Lady Thaw; deeming it odd that their loud voices hadn't summoned them with an explanation of why they were intruding on somebody's private area without invitation.

"Don't know. Let's try back at the reception," Martha suggested as she turned on her heel and retreated towards the lift, with the Doctor following her. Katy was about to follow them when she suddenly sees a skeletal leg with a ladies shoe on it, sticking out from behind a nearby desk.

"Uh, Doctor? Martha?" Katy calls out to them, grabbing their attention as she walks closer to investigate. She freezes immediately when she sees the gruesome discovery. "Woah!"

"Is that Lady Thaw?" Martha looked horrified.

"Used to be," the Doctor nodded, darkly. This situation was getting worse by the moment. "Now it's just a shell. Had all the life energy drained out, like squeezing the juice out of an orange." He grimaces sympathetically, despite his initial dislike of the elderly woman. Nobody deserves to die this way.

"Lazarus?" Katy guessed.

"Could be." The Doctor was vague, but not completely dismissing the idea.

"So he's changed already?" Martha questioned, but the Doctor shook his head.

"Not necessarily. You saw the DNA. It was fluctuating. The process must demand energy. This might not have been enough…" He immediately heads towards the lift with Katy and Martha following him rapidly.

"So he might do this again?" Katy asked, and the Doctor nodded.

"Uh-huh. But there's no 'might'. He will do this again, I'm sure of it."

Reception Room

Guests were still standing about in groups, drinking, laughing and gossiping with their friends, and remaining completely oblivious to the fact that they were potentially in quite serious danger … from their host. The Doctor, Katy, and Martha hurried into the room, looking around the room for a glimpse of Lazarus.

"I can't see him," Martha confirmed.

"He can't be far. Keep looking!" the Doctor urges her, and all three of them walk as casually and as calmly as possible around the room, as to not draw attention to themselves. Leo spots them and come over to speak with a visibly distracted Martha.

"Hey, are you all right, Marth?" He asks his sister, slightly concerned by how agitated she looked. "I think Mum wants to talk to you." He added, and Martha grimaced as the very last thing she wanted to do was talk with her mother; she knew the topic of conversation was going to be about the Doctor and Katy, and Martha would have to be a fool not to notice that Francine didn't exactly approve of her new friends, if the probing questions she had thrown at them earlier made evident.

She quickly changes the subject.

"Have you seen Lazarus anywhere?" She asks Leo, who frowns and glances around, trying to be helpful.

"Yeah, well, he was getting cosy with Tish a couple of minutes ago." He relayed and Martha's eyes widened in alarm.

"With Tish?" She parroted, and Leo nodded looking slightly confused by her alarm. The Doctor, who had overheard Leo's response, sharply jerks his head in his direction. Katy quietly swore underneath her breath; even more so when Francine chose this moment to interrogate the Doctor when she sees him, Martha, and Katy talking with Leo.

"Ah, Doctor…" Francine greeted him with a clipped tone in her voice. However, the Doctor easily ignores the older woman, focusing on Leo still.

"Where did they go?" He demanded urgently. Leo blinks at him in surprise.

"Upstairs, I think. Why?" Leo replied.

"Doctor—" He grabs Katy's hand, and both brush by Francine in their haste, causing her to spill her drink. Martha follows them. "—I'm speaking to you!" Francine snapped angrily at the Doctor, who ignores her.

"Not now, Mum." Martha firmly shuts down her mother as she jogs to keep up with her friends.

Katy looks over her shoulder and mouths the word 'sorry' to Francine who merely glowers at her and flounces off to get a napkin to dry off her arm. Leo rolls his eyes at his mother's melodrama and goes to find his own drink.

Lazarus's Office

Unaware that he had offended Francine with his actions, the Doctor returns to the scene of the crime in Lazarus's office, with Katy and Martha in tow. It was a race against time to find Tish before Lazarus could drain her of her energy like he had done with his wife. Martha was understandably worried for her older sister's safety, and looked impatiently at the Doctor for directions to where Tish and the mutated Lazarus were.

"Where are they?"

"Fluctuating DNA will give off an energy signature," the Doctor retrieves his sonic from his tuxedo pocket and starts adjusting the settings on it. "I might be able to pick it up." He starts scanning the area with his sonic before eventually pinpointing something when he scans the ceiling above them. "Got him!"

"Where?" Martha pounced. The Doctor merely pointed towards the ceiling, causing both girls to frown.

"But this is the top floor," Katy pointed out, then gasped in realisation.

"The roof!" both she and Martha exclaimed in unison before they stampeded for the staircase that would lead them to the roof which overlocked the London skyline.

The Doctor follows after them.

A/N: Stay tuned for part two