Hello, everyone! :D Warrichan here. I'd like to point out a few things about this fanfiction first.

1. This fanfiction is co-written by me and my sister.

2. It takes place around the end of Season Four, specifically between The Next Doctor and The Waters of Mars.

3. It's rated T for blood and dying, like the regular show.

4. You must be prepared to cry at any point in the story.

Thanks for your time! I hope you enjoy Catalyst!

Episode One: Convergence

In which the Doctor encounters a clever girl, aliens secretly attempt to mutate humans, and Kya joins the Doctor on his travels

The Doctor

I let myself fall into the ragged seat, letting out a puff of air. The TARDIS is quiet and still. I drum my fingers on the edge of the seat and let out another deep breath. I'm bored, not to mention lonely, and am really in need of something to cheer me up.

Basalonia! Brilliant idea. I spring to my feet and walk over to the controls.

I fly the TARDIS much more cheerfully now, grinning to myself. The grin is soon wiped off my face when alarms begin beeping frantically. Eventually they stop, and the TARDIS lands.

"We-ll," I say, poking my head out of the TARDIS. Then I frown. "Not Basalonia. Most certainly not Basalonia."

I step out onto the lawn. Looks like a college courtyard to me, maybe... early 21st century. Earth. Not Basalonia. "Hum," I say to myself, wondering if there's a good chip shop around here somewhere. I shove my hands into the pockets of my brown trench coat and begin to meander in a general direction chosen at random.

Kya

I'm sitting by the professor's desk during the lesson when I hear a strange whooshing sound from just outside the school.

I frown, my curiosity increasing with every passing second. I'm itching to go out and see what it is, but I can't. I lace my fingers together and sigh softly, trying to focus. The whooshing sound dies away.

Finally I can't take it. I stand up and quietly exit the room, hoping the students and my professor will just think I've just stepped out to use the restroom. Once I'm sure nobody can see me, I break into a run. I head outside and see a man with fairly spiky hair walking around, looking about him with his hands tucked into the pockets of his brown trench coat. There's a blue box with "POLICE PUBLIC CALL BOX" written across the top.

"Hey! Who are you?" I say, walking toward him.

He turns around, eyebrows raised. His dark eyes take in my simple lavender shirt, dark pants, reddish hair pulled back with a green headband, and glasses. "Hello!" he says with a grin. "I'm the Doctor. Who are you?"

The Doctor

Not a Basalonian, I add to myself.

"Kya," she says. "What are you doing? And what's that?" She points at my TARDIS.

"Me? I'm just looking for a good chip shop. Have you got any 'round here? One that makes 'em all hot and greasy." I pull my hands out of my pockets and rub them together, then pause. "Not that they would sell them wrapped in newspaper. They used to do that, but not anymore. I liked them wrapped in newspaper."

The young woman – Kya – seems rather perplexed. "What? Um, I'm not sure I know anywhere. Sorry. And you didn't answer my other question. What is that?" She points at the TARDIS again.

"Police box," I say, grinning. "Can't you tell?"

"Yes, but they're obsolete," she protests, "and how'd you get it here?"

"Obsolete!" I cry, feigning displeasure. "My police box, obsolete! Well, I never! You know, someone really ought to tell me before they go and make things obsolete." I shake my head and lean against the TARDIS, raising one arm over my head.

Kya crosses her arms, clearly fighting off a grin. "I would've thought you knew. Police boxes haven't been used since the 1970s, sir... what did you say your name was?"

"Not 'sir'. Just the Doctor," I say with a short nod.

"All right, Doctor," she says with a shrug. She walks closer to me and the TARDIS and starts circling us slowly, gazing at the TARDIS through narrowed eyes.

I pat it affectionately. "See?" I say. "Police box. Are we done here? 'Cos I'd really love some chips."

"...Yeah," she says after a pause. "Do you have any money?"

"Nope," I say cheerfully. "Haven't got a penny. I never have."

Kya stares at me like I'm crazy. "How do you expect to get chips, then?" she says finally, rolling her eyes.

I shrug. "I'll see when I get there!" I say with a grin.

She looks dangerously close to smiling. "Er, okay," she says, looking closely at the TARDIS once more – to avoid my gaze, I suspect.

"So, chips, then," I say. "Which way's the town? Or city, or station?" I push off of the TARDIS and walk a few steps away.

She points off into the distance with her right hand, lightly brushing her fingers against the TARDIS where I was standing with the other.

I smile. "Allons-y!" I say, heading toward it.

She stares at me. "Er."

"That's French," I tell her. "Means 'let's go' or something of the like."

"Yes, well, I know that."

"Then let's go. Allons-y!"

"I-I can't," Kya stammers. "I've got to get back to my class... And..."

Then she does something strange. She steps forward and grabs my hand with her right hand. Her slim fingers run over my palm for a few moments before she lets go, stepping back. "I'm sorry," she says again, and I vaguely notice that color blooms on her cheeks as she speaks. "I can't."

I stare at her, one eyebrow raised questioningly. "Alright, then. You'll miss out on the chips, though."

She shrugs and turns away, and I notice she's holding herself carefully so that her hands don't touch anything. She walks quickly toward the school.

I wait until she's off a little bit, then follow her surreptitiously. Why is she so interested in the TARDIS? Why isn't she deterred by the TARDIS's perception filter that makes people ignore it?

I stop for a moment as another thought strikes me. Perhaps she isn't human at all... an alien infiltrator?

Kya enters the school and I follow. After a quick glance around, I sonic the door for good measure and follow her down the hallways.

I pause when I see a door that proclaims "WARNING: RADIOACTIVE. DO NOT ENTER." That's odd. What are they doing with radioactive materials in a university?

I grin. There's nothing I love more than a keep-out sign! I'll have to come back for this, right after I find out if Kya –

I look up. Kya!

She's disappeared. The hallway is empty. "No!" I say. "No, no, no!" I run my hands through my hair, eyes wide with disbelief. I lost her!

Oh, well. No time like the present. Why don't I just try going in there now? I sonic the door, then carefully step inside, closing the door behind me.

"No. Way." I say, then wince. Oh, Donna... That's still a new loss for me.

I shake my head. "This should not be here," I mutter to myself, looking at the technology around me. Looks like someone's experimenting with... no. "Can't be," I say, pulling my glasses out of my suit pocket and slipping them on to peer at a test tube.

I pick up the tube, sniff it, and lick the rim. With a shudder I almost drop the vial. "Yuck, yuck, YUCK!" I shake my head, grimacing. So much for chips, I think darkly, slipping the tube into my pocket for further inspection. But oh, there's no mistaking that taste. Not in a million years – or at any rate not in 500.

I run a hand through my hair again and tuck my glasses back into my pocket, then after a quick scan with my sonic screwdriver I slip out of the room.

Kya

As soon as I get in the school I fast-walk straight to an empty lab. I scan my right hand for DNA samples. Once I'd separated my DNA from the Doctor's, I scan the Doctor's.

NONHUMAN

My eyes widen. "That's not possible..." I whisper. I scan it again, half hoping the scanner had made a mistake.

NONHUMAN

"That's not possible! It simply cannot be possible!" I shout. I scan the DNA I'd picked up off the box from where the Doctor was leaning.

NONHUMAN

I pull my hair back, then release it, heart pounding. Nonhuman? That means... he's not... Something about him must be different. He must just look human... Two hearts, maybe?

I shake my head, laughing at myself. Two hearts? What a ridiculous thought.

I walk quickly out of the lab and bump straight into someone. "Oh, sorry," I begin, looking up at the person I bumped into.

A man with brown, spiky hair, freckles, and dark brown eyes. "It's you!" I exclaim.

"Hello!" he says with a disarming smile, tucking a small cylindrical object into his suit.

I step back, unnerved. "W-what are you doing in my school?"

"Oh, this is your school? What a coincidence." He pulls out a battered leather wallet, flipping it open and holding it toward me. "Doctor John Smith, safety inspector."

"Uh-huh. Right. And you expect me to believe that," I say, unconvinced. I cross my arms and glare up at him, regaining my composure.

"My credentials are right here," he says, sounding offended.

I stare hard at the paper and the words blur before my eyes, eventually fading. Psychic paper, I think, unknowingly muttering something about aliens.

He frowns. "What's that?"

"You're not human," I say, looking up into his dark, admittedly beautiful eyes.

He looks back at me. "No, I'm not," he says, then narrows his eyes. "The question is: are you?"

"Yes," I say softly. "I am."

"Are you? Are you really?" he asks me quietly, leaning closer until we're inches apart.

"I promise you, I'm human. I'm just cleverer than most," I reply, trembling slightly at the intensity in his gaze.

The Doctor stares at me for a moment longer, then steps back, and I can breathe again. "All right, then. I believe you. Yes, I'm an alien. But I really can't stay and giff-gaff. There's something in this school that isn't right, and I need to stop it."

"Let me come with you," I say immediately. Just when I thought my heart rate was slowing down...

"Well, that's just the thing," he says. "Where I am I going? Right now, I haven't the slightest idea. Tell me – who works in that room right there?" He points to the door marked "WARNING: RADIOACTIVE. DO NOT ENTER.", the door he'd just come through.

"Er... Professor Jones," I say.

He winces, much to my confusion, but doesn't elaborate on why. "Take me to him... or her."

"Him. And we'd better wait until classes end, then he'll go in there... Wait, how'd you get in that room anyway?"

"Uh, sonic screwdriver," he says, pulling out a silver cylindrical object with a blue tip. "Very useful."

"Can I see that?"

The Doctor hesitates, then places it in my outstretched hand. I examine it closely and hold it up to the light, eyes wide with wonder. "Wow! This is really interesting." I start muttering to myself about how it must use ultrasonic frequencies to operate, running my fingertips lightly over the bumpy metal surface.

He grins. "Ultrasonic frequencies, yeah," he says, confirming my guess.

I smile up at him. "Here you go," I say, twirling the sonic screwdriver in my fingers before handing it back to him.

He slips it back into the inside pocket of his suit just as firm footsteps echo through the hallway. I see for a fleeting moment a figure rounding the corner before the Doctor grabs my wrist and pulls me quickly into a shadowed corner, wrapping his arms around me as he presses himself against the wall.

My face flushes as we stand awkwardly close in the darkness. "What are you doing?" I murmur, my lips barely moving and my voice hardly more than a breath.

The Doctor just raises his eyebrows at the man who stops at the "RADIOACTIVE" door. "Professor Jones, I presume?" he exhales.

I nod slightly, my hair brushing his chin as I do so.

We watch the professor open the door and enter the room. As he closes the door he turns around, almost looking straight at us. The Doctor jerks me closer, smushing himself in the corner. I push myself against him, trying to make myself as small as I can. My face is pressed into his shoulder now and my hands are on his chest.

My eyes widen as I feel his heartbeat – under both my hands. Two hearts?! I was right, then! Two hearts! That's remarkable.

Concentrate, Kya. Concentrate.

Finally the professor closes the door, and I can breathe again.

The Doctor

Kya immediately pulls out of my arms and steps several paces back. Her cheeks are bright red with a blush. I grin and pat her shoulder as I step past, then after a moment or two knock cheerfully on the lab door.

Kya rolls her eyes and stands behind me, pressing her shaking hands to her cheeks. I smile at her and knock again, seeing as there's no response.

The door opens and the annoyed-looking professor stands in front of us. "Who are you?" he demands of me, then sees Kya. "And what are you doing here? Aren't you Stalman's aid?"

"Yes, well..." she says awkwardly, her hands dropping from her face quickly. "This is, um, Doctor John Smith." She looks at me expectantly.

"Yes, John Smith, safety inspector," I say, flashing my psychic paper.

"We aren't due for an inspection." Jones frowns.

"Surprise inspection!" I cry happily, unruffled. "Pop inspection – you're a professor, right? So, like a pop quiz, but a pop inspection!" I smack my lips together at every 'pop', grinning again as I see Kya look down at the floor to hide her smile.

The professor frowns again, sliding out of the room and closing the door behind him. "Um, I'll show you to the students' lab," he says.

"Actually," I say, "I'm very interested in what might be in that room." I point to the door behind him.

Kya bites her lip, staring at the door, and I share her worry, though I don't show it.

"You can't go in there," the professor says. "The university is funding research on some experimental radioactive materials. Not accessible to the general public for safety reasons, of course."

"But he's a safety inspector," Kya cuts in pointedly, crossing her arms. "This is his job."

I nod appreciatively at her. "Safety inspector," I agree. "Safety is my business. I practically breathe safety. Safety is my middle name – and I'm serious about that. John Safety Smith. That's me."

Professor Jones looks at me like I'm insane. "I'm sorry, where did you say you were from?"

"Er, the Bureau... of Safety Inspectors," I say. I lean in and add conspiratorially: "We're rather new, actually. You may not have heard of us." Then I whip out my wallet again, waving the psychic paper at him. "But here are my credentials."

Kya leans around me to see my wallet.

"See?" I say, pointing to the blank page. To the professor it proclaims how my inspection has been sanctioned by the government, etc. But to Kya, it says something else.

Hello! This is psychic paper

Kya looks at me, startled, then turns to the Professor. "See?" she says, echoing me. Her hands are trembling again, and she quickly pushes them into the pockets of her black pants.

"Anyway, I have semi-direct orders from our prime minister," I continue. "That'd be Lemony Snicket, you know." I look to see his reaction.

Kya smirks, while the professor looks quite confused rather than annoyed now. "Oh, yes, Prime Minister Snicket, of course," he says, recovering.

I give a short nod. "Well, I suppose I'll start in the cafeteria. Nasty things, those are. Talk about a safety violation! And a taste violation, come to think of it. C'mon, Miss Kya."

She nods. "Follow me, Doctor John Safety Smith," she says, clearly having trouble containing her laughter.

"Right behind you!" I say, winking. Kya leads me out of the building to the TARDIS.

She stops me as we approach it. "Are we really going to the cafeteria? Cause they've got some pretty good chips."

"As tempting as it is, no," I say. "We're going to take a look at this!" I pull the vial of blue-ish goop out of my pocket with a flourish.

"Ooh! Where'd you get that?"

"Mad scientist Jones' lab," I say, eyes wide and fingers wiggling spookily.

Kya laughs. "You've already been in there?"

"What do you think I was doing in the school in the first place? Having a nice cuppa tea?"

"Looking for chips, actually, since that's what you told me you were here for."

I wrinkle my nose, remembering the vile-tasting liquid. "No, no chips in there at all," I say, then continue on toward the TARDIS.

She follows along. "Where are we going?"

"Back to the TARDIS," I say happily, forgetting that this is Kya – not Rose or Martha or Donna – and she doesn't know about the TARDIS yet.

"The what?" she says softly. "Do you mean your police box? Is that what you call it?"

I step up to it. "The TARDIS," I say with a nod. "That's Time and Relative Dimensions in Space." I open the door and walk in, leaping up the stairs to the main controls. I carefully pour the vial's contents into the TARDIS's analysis chamber and start it up, then turn to see Kya's reaction as she enters the TARDIS for the first time.

She's got a huge grin on her face as she wanders around, laughing quietly. "It's bigger on the inside! Oh my gosh!"

"It's smaller on the outside, actually," I say, grinning.

"Oh, isn't it the same thing?"

"Not with the TARDIS." The analysis alarm sounds, and I turn to the screen.

"Er..." Kya walks over to me. I can see her hands shaking a little. She peers at the view screen with me.

"Those," I say, pointing at the jumbled, intricate shapes on the screen, "those are squigglies. Now, there are good squigglies and not-so-good squigglies, and those ones are absolutely very not-so-good squigglies."

"Oh," she says, squinting at the screen. "Squigglies, eh? What do they mean?"

"They mean..." I begin, flipping a switch and taking out the vial, "they mean they mean they mean..." I snap the cap on the tube, slipping it into my pocket. "They mean we have a bit of a problem. End of the human race, that sort of thing."

"A bit of a problem? You call the end of the human race a bit of a problem?"

"Juuuuust a bit," I say, nodding. "But don't worry." I turn to her, eyes sparkling. "Don't you worry at all."

She looks into my eyes, clearly worried even though I just told her not to be. "Can you help? I mean, can you stop that from happening?"

I lean in close to her, studying her face. Glasses, freckles, light skin, sky-blue eyes, framed by reddish-brown hair. Then mine breaks out into a grin. "Oh, yes. I'm the Doctor, and Kya, I'm going to save your planet."

Kya

I grin back at him. "Then I'm going to help you, Doctor."

He claps my shoulder, leaning back (much to my disappointment, though I try not to show it). "Then, allons-y!"

I hug him quickly, for just a moment. "Allons-y! Where are we going?" I say, laughing a bit.

His cute grin widens. "Oh, we've got an alien mad professor to deal with. You game?"

"You bet I am!"

"Thought so," he replies, running down the stairs and flinging the TARDIS doors open. I run after him, shoving bits of my hair out of my face and smiling. We run through the school, and eventually the Doctor stops at the lab door, sonicking it quickly.

The door clicks, and he opens it. The room is empty. Not just empty as in nobody's there, but empty as in nothing. No test tubes, no alien tech, nothing. Just empty tables and a couple other things.

The Doctor sucks in a sharp breath of air. "No! No, no, no, no, no, no!"

I stare at him, eyes wide. "It's all gone. It's all gone, he's taken it all," I say disbelievingly. "But how?"

"No, no, no! Can't be," he mutters through clenched teeth. He runs his hand through his spiky hair. "Think, think, think! Er!"

"What do you think he's done with it?" I twirl a strand of hair around my finger.

"Hold on," he says, whirling around. He holds up his sonic screwdriver, activating it in short bursts. "Ha ha! YES! Kya, you're brilliant!"

I grin. "I am?"

"Absolutely brilliant!" he exclaims. "You're exactly right: What has he done with it all? We were gone for, what? Five minutes? Ten? There's no way he could have cleared everything out in that short time. Not unless he had a teleport, that is!" He turns, following the beeping of the screwdriver.

I comb my hair with my fingers quickly, following him. The beeping increases rapidly, and he stops. "Aha!"

"What? What is it?" I say.

"A teleport," he says with a grin. He quickly turns the screwdriver's dial and points it at the square-ish object in front of us that looks suspiciously like a mini-fridge. "HOLD ON!" he yells, grabbing my hand and pulling me up with him as he leaps on top of it.

"What?! What are you doing?"

"This!" The screwdriver whirrs but is soon overpowered by a whooshing noise. The room before us fades, another taking its place, but I don't give myself time to see it because I have my eyes squeezed shut. I grip his hand.

"Where are we?"

"Hmm, not sure yet," he says. "But my guess would be the Qwuvacian ship."

"The Qwuvacian ship?" I say, opening my eyes.

"Oh, yes," he replies, stepping off the teleportation pad. I notice rather awkwardly that he's still holding my hand. The room is dark despite brightly coloured lights on the walls and curved ceiling.

I step off a moment after him, then let go of his hand. "What's a Qwuvacian, exactly?"

"That," he says, pointing, "is a Qwuvacian. A not so very happy Qwuvacian, by the look of it, too."

The alien comes sauntering up to us. "Hello!" I say.

"How did you get on our ship?" the Qwuvacian says.

"How did you get on our planet?" The Doctor counters him easily, frowning as he says, "A bit out of the way from Qwuvacian space, don't you think?"

The Qwuvacian looks taken aback and a little angry.

"Ohhh, is that it, then?" the Doctor says knowingly. "You were banished, weren't you? Broke one of the many rules of the Qwuvacian order, did you?"

"So, what'd you do?" I say. The Qwuvacian glares at the Doctor, refusing to answer me.

"Ah, don't feel bad," he says. "The Order's got too many rules, if you ask me. I mean, really, 'there is to be no standing upon one's head on the third rotation from sun-up to sun-down? It's ridiculous!"

I lift a hand to cover my grin, but unfortunately the alien notices. "You are mocking us!" he says.

"Mocking you? Hardly. If I was mocking you I might have told you how veryfoolish it was to have come to this planet in the first place, and how it was very, very daft of you to even think of harming these people, these human beings, without running into trouble. That's what I would have told you if I was mocking you."

"NOW YOU ARE MOCKING US!" the Qwuvacian yells.

"Doctor!" I snap.

He ignores me and continues. "The fact that you could even imagine you'd get away with mutating a whole race is unbelievable. Now I'm giving you one chance. One chance to turn around and leave these people alone. What do you say?"

"We will not! Not when we have come so far!"

The Doctor

"Come so far to do what? Murder and enslave an entire population?! Call yourselves Qwuvacians? Pah! You should be ashamed of yourselves! Now, take this chance to redeem yourselves," I say earnestly. "This has to end now. You know it does. So stop with all this too-late-now rubbish, all right?"

"I do not know that it does! I do not..." He frowns. "It is too late. That is what they say. It is too late to stop, and you must die."

"No. No! Not too late. Never too late." I step in front of Kya protectively, blocking her. "You still have the chance to do what you know is right. Deep down, you know how terribly wrong this is. Qwuvacians never forget."

"I cannot... I cannot decide."

"You must," I urge him, staring at him intensely. "I can help you. Please. Let me help you."

The Qwuvacian frowns, anxiety and indecision written across his face. "I do not... This is not something for me to decide."

Kya blinks. "What do you mean by that?"

"Ohhh. You've got mates, haven't you?" I say in realization. "How many are you?"

"Many," he says vaguely.

"Many?" I say. "How many many? Just a few many or –" I spread my arms wide to illustrate " – many many?"

The Qwuvacian shakes his head. "Not many, many," he says. "Just a few, many."

"Ah, well. Just a few many." I turn to Kya. "I think we can deal with just a few many, don't you?"

"I think we can," she says with a grin, nodding.

I clap my hands together. "So, introductions! I'm the Doctor and this is Kya. What's your name?" I ask the Qwuvacian. "I do hope it's something she can pronounce," I add.

She rolls her eyes. "I could pronounce 'Qwuvacian' my first try, and I'm also a physics professor's aid. I'm pretty sure I'll be able to pronounce his name."

"Hmm, I should take you to Jvaliiikxyr," I say thoughtfully. "You might get along well in the Archive of Pronunciations and Enunciations."

"Maybe you should. Anyway, what is your name? You didn't say," Kya adds, turning to the Qwuvacian.

"My name is Bo," he says.

Kya glares at me.

"Oh, is that all?" I say. "Well, it's nice to meet you, Bo. Normally I'd invite you out for some chips, but I'm afraid we have a bit of a problem at the moment."

"Yes, we do, and we need your help," Kya says. "If you're willing to help, that is."

I put my hand on Bo's shoulder. "This is your choice, Bo."

After a moment of thought, Bo says, "I will help the Doctor and Kya."

I grin at him. "Good lad," I say. "Now, how are they planning on spreading this serum?" I pull out the small test tube and turn it over in my hand thoughtfully.

"Central diffusion," Bo says.

I bring a hand up and run it through my hair. "Central diffusion..." I repeat.

"Central diffusion?" Kya echos.

"Spreading the mutation particles throughout the planet's atmosphere, so that it'll fall like precipitation. Deadly rain," I explain grimly.

"Er. That's not good. We have to switch the mutation particles with something else."

I snap my fingers at Kya. "Do you see?" I say to Bo. "She's brilliant! Absolutely brilliant." I flash a grin at her.

"But what can we switch it with?" Kya continues as if I never spoke. She starts pacing, twirling a strand of her reddish-brown hair around her finger.

I raise my eyebrows at Bo as we stand and watch her. "Now she's going!" I whisper to him.

"Er... Something that looks enough like that." She points at the test tube in my hand. "It has to be able to deceive the Qwuvacians long enough so that they won't notice anything is different until it's too late to do something about it. So we've got to make an artificial substance that resembles the mutation serum."

"Goop!" I add with a grin. "Technical term, that one. We need goop, and lots of it."

"Goop!" Kya repeats, turning to me with a huge grin on her face. She points at me.

"Exactly!" I exclaim happily, pointing back. Then I turn to Bo. "You wouldn't happen to have any goop on board, would you?"

Bo looks at me askance. "Goop?" he says.

Kya snaps her fingers suddenly. "Engine oil plus food colouring –"

"– equals goop!" I finish, laughing. "Brilliant!"

I pause, fishing around in my trench coat pockets. "Let's see..." I say, pulling things out and then putting them back as I identify. "Wind-up mouse... matchbox... paintbrush – oh, remind me to give that back to Leonardo next time I see him... ah, here it is!" I pull out a small bottle filled with brightly coloured liquid.

Kya's staring at me with half a smile on her face. "Let me guess, your pockets are bigger on the inside too, aren't they?"

"Oh, yes," I beam, patting my sides. "Now let's go make us some goop! Bo, lead the way!"

Bo nods and starts walking back the way he came, glancing around warily. Kya follows and I bring up the rear quietly. We step into a turbo-lift and make our way down to the engine rooms.

Kya

"John Safety Smith?" I burst out while we're in the lift. "I've been thinking about that ever since you said it. Seriously, even the John Smith part was too obvious. But Doctor, John Safety Smith?"

"It's a good name for a safety inspector, don't you think?"

"Oh, come on!" I say, trying not to laugh. "It basically screams 'fake'! Well, to me, at least."

The Doctor looks at me thoughtfully. "That's what I don't quite understand. Most people will pass over John Safety Smith as an oddity and move on – just like the strange blue box standing on the street corner. Part of that's because of the TARDIS's perception filters. But for some reason, it didn't seem to faze you. Why?" He seems to be talking more to himself than to me.

"Is that why you thought... you thought I wasn't human?" I ask, meeting his eyes.

"Yes," he says simply as the lift comes to a stop.

"I don't know," I say quietly, shrugging. "I suppose it couldn't just be because I'm clever." I say this half-jokingly.

Brow furrowed, the Doctor shakes his head. "No, it's not that," he says. Then, catching the look on my face, he adds quickly, "I mean, you're brilliant, but there's something... more... about you." He studies my face intently.

I shrug again. "We'll discuss this later," I say, my heart beating faster.

"Right," he says, and I notice – to my embarrassment and delight – that he seems to be having trouble looking away from my face. He steps out of the lift, clearing his throat and ruffling his hair quickly as he glances away. "Right," he repeats. "Goop-making time."

"Yes," I say, turning my eyes downward. "Right. Good. Goop-making time. Let's get started." I step out after him. Bo is watching us with a look of clear confusion on his face.

"Which way's the engine fuel reserves, Bo?" The Doctor licks his finger, then holds it up in the air, turning and then stopping. He points the way he turned. "Hmm, this way, right?"

"Yes. That way," Bo says, walking in that direction. We follow him to a hot, steamy room. Right smack dab in the center, leaving hardly any room for anything else, is a giant bronze vat.

"Oh. Oh, dear. Is that..." I'm speechless.

The Doctor grimaces. "The mutation serum, yes." We walk around it carefully and reach a door on the other side.

Bo tries to open the door but it's locked. I look at the Doctor expectantly. He grins and pulls out his sonic screwdriver, turning the dial and aiming it at the door's control panel. I pay careful attention to the setting, making a mental note of it in case I ever have to use the screwdriver.

The door swishes open and we step into a huge room filled with tanks. "Engine fuel," the Doctor says satisfactorily. "It's amazing how much of this stuff the ship burns up in a day." then he pauses, a shadow passing over his face. He looks at Bo sadly. "If we use this, you may not have enough for the journey home."

I look back and forth between them, startled. "What will you do then?" I say quietly.

"I can't let you take this risk, Bo. We can find another way."

"No," he says firmly. "We must save the humans."

The Doctor bows to him in the Qwuvacian fashion. "Thank you. Thank you from the bottom of my hearts," he says.

I carefully copy the Doctor's bow as best as I can.

The Doctor takes a deep breath. "Well. Let's get started, then." We make our way over to the ladder of one of the tanks.

"You do know what you're doing, right?" I say.

He starts to climb up the ladder. "Oh, yeah... No, not really, actually."

"Me neither. I'm going to assume you just pour in the food colouring?"

He considers it, then nods. "Sounds about right, yeah," he agrees.

I roll my eyes and grin, looking up at him. "Go ahead, then."

He reaches over the top and leans precariously over the side. Unscrewing the top, he pours the dye in. I watch, on tiptoe, sticking my hands in my pockets nervously. I can tell it's clearly not enough.

The Doctor reaches for his screwdriver, and I bite my lip as he wobbles a little. "Careful!"

He looks down at me. "Oh, yes, because I was planning on taking a little swim in this engine oil," he says sarcastically. He aims the sonic at the oil and, after changing the setting, presses the button, holding it down for a few seconds. Then he turns it off and sticks it in his pocket.

I roll my eyes, gritting my teeth. "Shut up."

"Now," he says, coming down the ladder. "We need a pumping tube. Bo?"

"I will get one," Bo says and starts walking around looking for one.

When the Doctor is safely on the ground, I let out a breath that until then I hadn't even realized I'd been holding.

He grins at me quizzically. "I wasn't going to fall in, you know."

"I know," I say, embarrassed that he noticed.

Luckily Bo comes back at that moment. "Ah, these are perfect!" The Doctor exclaims, taking one end of the tube and examining it. "Professional grade, too. Neat work, Bo."

"Can I help?" I say.

"Yes," the Doctor says, handing me one end. "Take this and put it into the goop tank. Bo, you hook these up to a generator and an empty reserve. I'll take these ends to the mutation vat."

I nod and climb carefully up the ladder as the Doctor and Bo both run off, then stick the end of the tube into the goop tank.

"Ready?" the Doctor yells from the other room.

"Ready!" Bo and I call at the same time.

"Here goes!" he shouts, and there's a motor-like noise as he activates the pumps.

I hold the tube in place, a little unsure of myself and hoping this is what I'm supposed to be doing. The goop starts travelling up the tube.

"Yes!" I hear the Doctor yell joyously, and I grin. "It's working!" The mutation serum, I assume, is being emptied out and being slowly replaced by the goop.

After a while, the goop is finally gone, safely transferred to the mutation vat. I climb down cautiously and join Bo as we walk to the chamber with the mutation vat. The Doctor looks down at us as we enter, smiling.

I smile back. "We did it! So, what's the next step?" I ask.

"Next –" he begins, but the ship lurches sharply to one side. Before any of us can do so much as blink, the Doctor tumbles off the ladder, landing roughly on the hard floor.

I stumble when the ship jerks, almost falling but catching myself just in time. I run over to the Doctor and kneel by his side. "Are you okay?"

He groans in response, wincing. He lays there for just a moment before leaping to his feet, and I scramble up with him. "Right," he says, rubbing the back of his head where he hit it. "We've entered Earth's atmosphere. Time for us to go."

I bite my lip to hold back the words I want to say. Are you sure you're okay? Instead I ask, "What about Bo?" He's watching us quietly, like usual.

The Doctor winks at me. "I've a spaceship/time machine. I think we can arrange something, just this once."

I nod and look at Bo. "Sound good to you?" I say.

"Yes."

The ship jolts again, and the Doctor stumbles to the lift. Behind us, the goop chugs violently. I grab Bo's hand and pull him into the lift with me. "Come on!"

The lights inside the lift blink, and the Doctor holds his sonic screwdriver up to the control panel to keep it from plunging down. From somewhere an alarm goes off, startlingly loud. "Not good," the Doctor mutters.

"What do you think that was? They haven't found out that the mutation stuff was switched with our goop, have they, do you think?" I say.

"Well, they sure know something's not right," he replies grimly. "And I'd prefer not to stick around for questioning."

The Doctor

"You're right, of course," Kya mutters, half to herself.

I choose to ignore that remark. "So, we'll just pop right back to the lab..." I trail off as the door opens, revealing a full regimen of Qwuvacians waiting for us.

"Or not," Kya says.

I go to shut the lift doors but it's too late. They've jammed them.

"What do we do?!" Kya says.

"YOU WILL SURRENDER, INTRUDERS!" the general says.

I put my hands up behind my head, since there are a dozen blasters pointed at us. "That answer your question?" I murmur under my breath.

Kya nods slightly. She and Bo put their hands up too.

They bring us to a cell, spitting "Traitor!" at Bo as they do so. Someone takes away my screwdriver, ignoring my cry of, "Hey, no! That's not a weapon!"

"So, they have the screwdriver, and the TARDIS is back on Earth. We're stranded up here," Kya sums up.

I sigh, plopping down on the bunk. "Basically, yes."

Kya sits beside me.

"I'm sorry," I say quietly.

"It's not your fault. Don't apologize," she tells me.

I look at Kya sadly, knowing that is indeed my fault she's here, trapped in a dingy alien brig and not at home doing... whatever it was that normal humans her age did.

She meets my eyes, and I'm struck again by how blue hers are. "Stop giving me that look," she says softly. "You're making me sad."

I look down at my hands and sigh again. The floor grumbles beneath us, and I look up sharply. "Wait," I say. "Hold on."

She stares at me. "What?"

I stand up and stomp on the floor. "Ha!" I cry jubilantly.

"What is it?" She jumps up beside me.

"What's under here?" I say. "Steam vents! Bo, you have a resonator, right? One they didn't take?"

Bo nods, pulling it out.

"Brilliant!" I cry happily. I take it and add a hypothermial ray to it (it's nice to have pockets that are bigger on the inside), then set the dial. I stick it onto the floor in the center of the room, then pause, looking up at the two of them.

"What is this going to do?" Kya asks. I can practically see the gears turning in her head.

"We're going to knock the floor out!" I exclaim, grinning. "Ready?"

She gives me a thumbs-up, and Bo nods again.

I slam the button and leap out of the way, shouting, "Allons-y!"

Kya jumps back quickly, right beside me. Bo steps away in the opposite direction. The pressure causes the floor to rupture, leaving a jagged, steaming hole.

Kya walks up to it and looks down. I come up beside her, peering down. Our heads close together, ears nearly touching, we look into the steamy glow. "Ooh," she says, smiling. "Nice work."

"We'll see about that," I say, but smile regardless. I carefully grab one side and lower myself into the hole, feet dangling.

"The floor isn't that far off, I think you'll be safe if you just let go," I hear Kya's voice from above me. "You've got long legs."

I puff with the effort, then drop down. I land somewhat unsteadily on a metal grate floor, and by the time I've regained my balance and turned around, Bo is already down as well. I stand below the hole, calling up to Kya, "All right, come on down."

She kneels and grabs the ragged edge, but quickly pulls her hand back, wincing. She moves her hands to a smoother part and swings down, letting out a short gasp.

"Hold on!" I say, stepping forward and wrapping my arms around her legs. "There, I've got you."

"Okay, I'm going to let go now," she says. Her voice shakes, and I can feel her trembling.

"Alright, I've got you," I repeat reassuringly, bracing myself and grasping her tighter.

Kya lets go, shrieking quietly as she slides down in my arms. I hold on to her even tighter so she doesn't fall. We end up at about eye level, her feet a few inches off the floor.

"Hello," I say, smiling.

Her face reddens. "Er. Hello."

I grin at her and set her down, turning to a bemused Bo. "Um, yeah," I say, gesturing to Kya, "she's down now."

"Yep, I'm down," Kya echoes.

"Definitely do–" I begin, turning around to look at her, but stop when I see her fingers. She's examining them with a look of pain on her face. There are several shallow cuts on them. "Oi, are you all right there?"

"Yeah, I'm fine. Just..." She points up at the jagged edge of the hole where she'd originally grabbed the side before moving her fingers. "That's sharp there. I'm fine, though. Let's move on."

I frown but start walking, telling myself I'll take care of that in the TARDIS's infirmary once we're out of here. Not that Kya's coming with me, of course.

I stop by a small porthole-door on the curved wall of the room, reaching for my pocket. Then I remember I don't have my sonic screwdriver.

Kya looks at me. "How are we going to get through?"

Bo steps forward and pulls out a strange-looking implement. "This may be necessary," he says simply, handing it to me. I turn it over and grin.

"What is that?"

"Demagnetizer," I say.

Kya smiles.

I plant the circular demagnetizer in the center of the door and take a step back. The disk opens into what looks like a tiny satellite, then with a puff of steam the door clicks.

Kya raises her eyebrows at me. "You first."

I yank open the door and poke my head into the tiny room beyond, then step into it. It's about a meter and a half around and consists of a metal ladder going up an opening in the ceiling.

"Well. This is small," Kya says behind me.

"Engineering shaft," I say. "They run throughout the whole ship. In about – we-ll – a thousand years or so from now they'll be called 'Jeffery's Tubes', but they're still just as small." I start to climb up the ladder, Kya and Bo following behind.

The ladder leads us to the small, tunnel-y shaft. It's only just big enough for me to crawl on my elbows and knees in. The hot, heavy air makes it difficult to breathe, and the orange and red lights on the sides make me feel dizzy. Kya and Bo crawl in behind me, and we start to move slowly along.

"Shouldn't be much farther now," I say for the third time. We've been going down the shaft for what seems like forever.

"Yeah, that's what you said five minutes ago," Kya pants.

"Well," I begin, gathering breath, "we are not... five minutes closer to being there... than we were five minutes ago." It's difficult to talk in here, and that frustrates me almost as much as our current predicament. I don't like not being able to talk.

"That doesn't make... any sense at all," Kya manages.

I let myself down, half-sitting and half-laying. "Yes, it does," I say. "Because we've been going in a big loop." I look across to see 'SECTION 5' – again.

"Ugh," Kya says, stopping when I do. "What are we supposed to do now?"

I sigh, then suddenly brighten. "Hold on," I say. "This is the engineering shaft!"

"Yeah," Kya says, wiping sweat off her face and leaving a smudge. "And?"

"That means all of the ship's systems run through here – most of them, anyway. Every section has an emergency teleport," I say, configuring the control panel. "Won't be enough to get us back to Earth, but it will be enough to get us to the teleportation room."

Kya's starting to look like she's in serious danger of passing out. "Well, let's try for that," she says. "This is bad for all three of us."

"Yes. Right." I breathe out, still punching in numbers. This would be so much easier if I had my sonic screwdriver.

A moment later I eject an exclamation of relief. The shaft begins to fade away, the teleportation room taking its place. Kya takes several breaths of relatively clean air, scrambling to her feet.

I stand and wipe my sweaty forehead with the back of my hand, leaving a smear of dirt. Then I stumble over to the teleportation controls.

Kya seems only able to stand for a moment. Then she sits back down on the floor, taking off her glasses and wiping the steam off them on a clean part of her lavender shirt.

I quickly configure the settings for two to beam down and set the coordinates for the school campus. "Bo, Kya, get on the pads."

They obey. "Doctor, you're coming, right?" Kya says.

"'Course," I say, "right behind you." But I know that someone will have to activate it, and without my sonic screwdriver to do it remotely... I smile at her.

She raises an eyebrow. "Doctor. No. You don't have your screwdriver. I'm not leaving without you."

"Oh, yes you are!" I say, slamming my hand down on the button.

"NO!" she screams, reaching for me, but it's too late. She and Bo disappear.

I run a hand through my hair quickly and make for the door. I almost walk into a couple of Qwuvacians in the supply room, but manage to duck behind a storage cylinder just in time.

I wait until the Qwuvacian turns away before poking my head up. There, on a metal table a few steps away, is my sonic screwdriver. I reach for it – but suddenly the Qwuvacian turns to leave the room, and I quickly duck back again.

He leaves, and his mate over there is nodding off, so I reach out and grab my sonic. Finally, I think, more than happy to have it again. Then I sneak out of the room, being careful not to run into the Qwuvacian who had already left.

I hastily look around for a control panel. There's one on the wall, and I hurry over to it. I sonic – oh, how nice it is to have my screwdriver back! – the control panel's bolted edges and rip the front off, revealing a mess of wires.

I put my glasses on and tear out a few wires, splicing some together and trying not to think about what Kya and Bo are doing.

Kya

Bo and I appear on the front lawn of the school. It's deserted; it seems the school day is over. I sink to the ground, eyes wide in disbelief. "We've got to get back up there," I say. "How can we get back? We could... we could..."

Bo watches me, face blank.

I jump up suddenly despite my exhaustion, eyes brightening. "I've just had an idea! Come on, Bo. Follow me!"

Bo and I run into the school and find the lab that's connected to the ship. I kneel beside the teleport, press a few buttons, flip a few switches, and connect a wire or two. Then I step up onto it and pull Bo on with me. "Here we go!" I say as we teleport back to the ship.

Once we're there, I look at Bo. "Should we split up or stay together?"

"Kya will find the Doctor," he says decisively. "Bo will make his people leave the human planet alone."

"All right," I say. "Good luck." I shake his hand and then exit the room, careful not to be seen.

It doesn't take me long to find the Doctor. Once I do, I walk quietly over to him and touch his shoulder. "Doctor," I whisper.

He jumps, startled, and looks over at me. He whisks off his glasses and shoves them into his pocket. "Kya! What? What?"

"Shh!" I say, but I can't help grinning. "Hello!"

"What?!" he says once more, although he does lower his voice. "But how did you get back here?"

I shrug, trying not to look guilty. "Messed a little with the controls on the teleport back in the lab. Reversed the coordinates, activated the teleport, that sort of thing. It was nothing once I thought about it."

He lets out a short laugh of amazement, shaking his head. "Okay, then. Let's go find the bridge. I have an offer for the Qwuvacians that they literally can't refuse."

"Oh," I say with a smile, "I like the sound of that."

He grins and waves his sonic screwdriver at me as we try to make our way to the bridge unnoticed. I nod, suppressing a giggle at the joy on his face.

"Right," he says softly as we come to the bridge door. He sonics it open and we step onto the operations balcony, which slightly overlooks the rest of the bridge.

The Doctor

"YOU ARE A FOOL, BO!" we hear someone say, the words closely followed by a blaster-fire. I look just in time to see Bo crumple to the floor.

"NO!" I yell, launching myself over the edge of the balcony. My feet sting at the impact when I land but I hardly notice. My scrambled run turns into a slide as I kneel at Bo's side.

He still has a pulse. I turn him gently over, then wince. His whole middle is torn up, drenched with his dark blue blood. "No..." I whisper, voice breaking.

"Doctor," he manages to say, spitting up blood.

"Bo, don't," I say.

He continues anyway. "Doctor, I did the right thing."

I nod, unable to see. "Yes, Bo," I tell him. "Yes, you did."

He gives a weak smile, then breathes his last. I close my eyes tightly, tears streaking clear paths down my dirty face. I pass my hand over his eyes, closing them, then tilt my head back, taking a deep breath. Suddenly Kya's by my side, tears brimming in her eyes. I stand up, angry and glaring at the Qwuvacian leader.

"You," I say to him, voice deadly serious. He raises his gun but I raise my sonic screwdriver. "Don't make me," I say, finger hovering over the button. "Don't even."

"Your device does not frighten me," he declares.

"Oh, yeah? Because it should," I spit. "I have it linked to your main reactor. One tap and the whole ship goes."

"You would not do that," the leader says, a little uncertainly.

"He would," Kya says sharply beside me. I look at her. Her sky-blue eyes are too big, too watery, but she lifts her chin defiantly and her voice doesn't even shake as she speaks.

"You tried to mutate and murder an entire planet and you just killed my friend!" I shout at him, looking back up. "So yes, I'd do it as soon as blink! But I'm giving you a chance. You don't deserve it, and right now I'm very, very angry. So if I were you, I'd take this chance right now while you still can."

"NEVER!" the leader yells.

"Then I'm sorry," I say, but before I can press the button, the Qwuvacian leader is struck from behind by the butt of a blaster-rifle.

He slumps down, unconscious. The general is standing behind him. "We will leave," he says, sounding weary and ashamed. The others nod in agreement, and the general heaves a sigh. "We have followed a fool."

I look at them. "I think you've been away from home for far too long," I say sadly. The general nods penitently.

I turn my gaze to Kya. She's biting her lip now, drumming her fingers against the side of her thigh. "Come on," I say. "Let's bring you home."

A few minutes later we're standing on the college lawn outside the TARDIS. "Well, I suppose this is goodbye, then," I say, trying not to sound regretful. I hate farewells, which is why I usually just leave before anyone notices. But I can't do that to Kya. I just can't. I shove my hands into my pockets and lean back onto the TARDIS, telling myself once more that it will be better for me to be alone. Better for everyone, myself included. I don't think my hearts can bear being broken one more time.

Kya nods, tears filling her eyes not for the first time today. "Okay," she says quietly, her voice choked. "Okay." She turns and walks away from me slowly, her fists clenched at her sides.

I force myself to turn away, to go into the TARDIS, to leave Kya behind. I start the TARDIS up sadly. Why did this have to happen – again?

The TARDIS takes off, and I sink into the battered seat. I rub the bridge of my nose with both hands. I remember Rose, and Jack, and Martha, and Donna, and even Wilfred; and just for a moment, I allow myself to remember past the pain of the emptiness they left behind, instead remembering the good, happy times. Then I picture Kya, standing there, trying not to cry but not really succeeding. I sit there, hands still on my face and mouth opened wide. I leap up, knowing what I have to do – what I want to do, despite everything.

I put my hands on the TARDIS controls.

Kya

My lower lip trembles. I had imagined myself doing so much with him, travelling the universe with the Doctor. By his side, forever. I'd imagined spending my life with him. Silly me.

I blink, letting the tears slide down my face. I walk faster, my vision blurred, and eventually come across a bench. I sit down hard, taking off my glasses and shoving them in my pocket. Stupid. Of course he wouldn't let you go with him.

I sob, lifting my hands to my face. I can't believe he's gone. I... I liked him. I wanted to stay with him but he's gone, he's gone. He just left, and I don't blame him.

My eyelashes feel wet on my cheeks. The tears slip through the gaps in my fingers and I let out a shuddering sigh, trying to stop crying but failing. Stop it, I think. He was just another man. Get over it. But every part of me knows he was more than just another man.

The Doctor

I step out of the TARDIS onto the now-familiar campus grounds. Kya's nowhere in sight, so I start running, searching for her.

I recognize the huddled figure on the bench immediately. I run over to her. She's crying, her face buried in her hands. I touch her shoulder. "Don't cry," I say softly.

She sniffles, clearly not recognizing my voice and not looking up. "Sorry, I just..." She sighs. "Nothing. It's nothing."

I sit down on the bench beside her, taking a deep breath. "Well, I can hardly believe it's nothing. You wouldn't be crying over nothing, now would you? You can tell me – maybe I can help you."

Her eyes fly open and her hands drop from her face. "DOCTOR!" she yells, the tears flowing faster down her face. She flings her arms around my neck, hugging me tightly.

My face breaks out into a grin, and at this moment all of the heartache in the universe couldn't have kept me from right here and right now.

Kya sobs into my shoulder. "I thought you were gone," she says.

"But I came back," I say, smoothing her hair. "I'll always come back."

She laughs through her tears. "I'd hoped you would," she says.

I stand and help Kya to her feet. "So... Chips?" she says with a giggle, rubbing her eyes and then reaching into her pocket. She pulls out her glasses and puts them on.

"Ahh!" I say, tilting my head back. "Chips! I could really go for some chips right now."

Kya laughs. "Okay, let's go get some chips, then."

I grin at her. "Allons-y!"