Author's Note: Here's the 15th and last of the 'Incompatible' series, at least for now. I have been working on another chapter story to go along with it, but I'm not sure how long it's going to take me to get going on it. Hope you enjoy!

Summary: The Doctor teaches Jon about time.

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The Teaching Planet

"Whatcha doin'?"

"Trying to land as softly as possible."

"But you're not supported to be landing the TARDIS when mummy's asleep."

"I know; that's why I'm trying to land very softly."

It takes only a matter of moments for Jon to get over the idea of breaking one of mummy's rules before he's shrugging and rushing up close to the console where he can watch his father work. The screen is angled up to make it easier for his father to read, but very difficult for him to get a good look at the symbols. Not that it would help him much; his written Gallifreyan is practically nonexistent, even if he is getting a very good grasp on the spoken language.

"Where are we?" he asks just as he sees his father's hand reach for the final landing sequence. It's the rolling dial, which he knows means his father is almost certainly going to spin it forward and slap his hand down on it to stop it with a flourish. Even so, he giggles when it happens and doesn't stop, mostly because his father has caught him around the waist and begun to relentlessly attack his only ticklish spot.

It's only when Jon's finally released and his feet have found the ground and the Doctor's walking away from him around the console that the Doctor finally answers his question. "We are at Nahym."

"Nahym?" Jon plays with the name in his head- he rather likes it. "Never heard of it."

The Doctor chuckles at that. Jon loves it when he laughs because, around him at least, he laughs with a smile on his face. "I reckon that there are a lot of places you've never heard of."

"True. So why are we here?"

"Well, mostly because I like it. But mainly because it's one of the oldest planets in the universe. And also one of the best places to learn."

His father, being a much taller man than Jon, needs only four excited steps to make it to the railing where he last left his trench coat. But this doesn't dissuade Jon from sprinting towards him, skidding as he stops by the railing. "Learn about what?"

The Doctor flattens himself up against the door, one hand on the handle, the other with his coat draped over it, and finds Jon's face. "Time."

There are about three million questions that burst through Jon's mind. He wants to know everything from how this planet it better at teaching time than a Time ship to what particular aspects of time he means to why tonight of all fifty-two nights that Jon has been begging to be shown the secrets of his time sense has his father picked this night.

But not a single word passes his lips because the Doctor, as if his one word was a secret password to open the door, threw it open and in Jon's line of sight he can already see why his father likes this place. He can see how old it is and how wonderfully unique and exotic this world must certainly be.

He doesn't get much time to truly take in the swirls of gold and purple and silver that are floating through the sky or the way the scarlet grass like plant shines in the sun or the way the trees remind him of weeping willows, only golden and mystical; because his father is already taking long strides away from the TARDIS and Jon has to scurry after him.

The Doctor stops only a few meters away from the TARDIS, right at the side of a river. He sweeps his long trench coat off his arm, lays it out on top of the scarlet grass and waits for Jon to collapse to his knees before doing likewise. Jon's on his stomach and crawling as close to the river as he dares by the time the Doctor's long body is lying beside his.

"Is the water naturally all those colours or are those some kind of creatures?"

"Look closely."

Jon does, bringing his face almost in contact with the water as his father chuckles behind him. "Definitely a creature." He looks back over his shoulder. "What are they called?"

"They're called the Baniti."

"They're cool looking."

"They're actually what we're here to look at."

"Really?"

"Yep. Watch the way they float atop the river. They're not moving—they have their own place."

"It looks like they're moving- it's just the colour right?"

"Yep."

"How do they do that?"

"The colours are a visual manifestation of their telepathic link to each other."

"Then they're sentient?"

"Not very."

"Why are we observing them?"

"See that one, right there in front of us?" Jon follows his father's arm down towards the water, his eyes falling on the exact Baniti that his finger is pointing at. "Watch it for a moment." And Jon does. It's sort of ovular shaped, and kind of pointed on one end, which Jon assumes is the "head". It's also rather transparent- he can make out some of the actual water- but, at the moment, it's a pastel pink. And then it transforms into light blue, and then pastel green.

"I thought we were learning about time?" Jon asks, even as he continues to watch as the Baniti becomes light red.

"We are. Think of each individual Baniti as a pocket of time. Each pocket has its own place in time, just as each Baniti has its own place on the river surface. And each pocket is fixed exactly as it is, just as each Baniti will always remain just as it is."

"But time can be altered."

"Can one of these Baniti be altered?"

Jon looks down at the same Baniti as he thinks before looking back us at his father. "They can grow. They can get sick. They could be injured by some outside force. They might have hormones that have a circular pattern."

"Very true. How might that relate to time?"

"Well," he looks away, "Time can be changed. People can make different choices in a pocket of time. Someone who travels through time could alter something."

"Right. But why do you think I said that a pocket remains fixed?"

"Because… The outcome is more important than the events themselves?"

The smile forms almost too fast on his father's face as he beams, "Excellent!" and Jon can't help but smile back. "Every moment in time can be altered slightly. Certain changes won't affect where that moment needs to go to connect to all other moments. See how each Baniti lines up almost perfectly. There's one creature behind, two to the sides, and one in front?"

"Uh-huh."

"Time acts similarly. Each pocket runs concurrently with millions of other pockets-"

"You mean like… those pockets are occurring at the same physical time, but in different places?"

"Right. One pocket might exist at point A at time 1 and another pocket might exist right next door, point B, also at time 1. That's represented by the two other Banitis on each side. Watch the colours- tell me about them."

They move, is the first thing he noticed about them. But, now that he's really looking, it's not so much that the colours move as each Baniti influences the colours. He watches the same Baniti again. When the Baniti behind it is green, it's still pink, but it only takes a few seconds for it to turn green itself. And then, only a few moments later, the two Banitis on either side of it have turned only slightly green but a whole bunch of Banitis in front of it have also turned green.

"How do you think that represents time?"

"Well… if something happens in one pocket, it's definitely going to influence the next pocket of time at the same place. And because now that pocket is different, the pockets at the same time but in different places may or may not be affected by those changes. But, because that pocket is different now, the pockets in front of it, mostly in the same place but also in different places, will be affected."

"You got it."

"So… if a pocket of time can be altered, then what causes all the problems?"

"A problem with time comes in when a pocket of time is broken- when something gets changed completely and suddenly the ending changes."

Jon watches as the Doctor brings his finger so close to the Baniti that he's almost touching it. Suddenly it seems to fold in on itself. "Defence mechanism," the Doctor says absently. "Watch was happens."

Suddenly the Banitis in front of the one are becoming completely transparent. Those besides them are becoming less vivid, losing some of the colour. The Doctor pulls his hand away and the Baniti unfolds and slowly colour returns to the chain.

"What happened?"

Jon glances at his father before looking back down at the Banitis. "Well… because the Baniti was no longer connected, it couldn't receive and send the telepathic impulses, cutting off the colour exchange. So… basically you broke time by doing that. If one pocket breaks, the ones it's touching will break and thus creating a chain reaction, slowly unraveling the entirety of time itself."

The Doctor's just smirking at him when he looks back up. "Yep. Now there's one other thing."

"What's that?"

"You know how sometimes we pop in and out of places, no worries? And sometimes we have to stay and deal with something?"

"Uh-huh."

"Explain why that is."

"Well," Jon has no idea, so he looks away. "I'm not sure."

"If we have to stay, what's usually happening?"

"Something unexpected."

"And what do you think might happen if that unexpected thing isn't dealt with?"

"It, em… might change the ending of that pocket of time."

"Exactly. Those pockets are known to be in flux. Something that hasn't ever happened in that pocket is now suddenly happening. Sometimes we find ourselves there to help sort it out. Sometimes time changes because of it. It happens a lot actually. The problem is, if a pocket is in flux, then it's very delicate and to attempt to rip through the pocket and into the Vortex isn't a very smart idea."

"So then… how do we leave?"

"We see the moment out, wait until we're at the very end of that pocket and sneak out through the small gap between moments."

"Yeah but… how do you know? How do you know where you are in a pocket? Is it the beginning, end, middle? How do you know when you've moved from one to the next? How do you know if a pocket's in flux or if it's supposed to be like that? You change things all the time but how do you know when that's okay?"

He stops mostly because he's running out of air and his respiratory by-pass isn't anywhere near developed enough yet to practically use, which is a shame because sometimes when talking with his father he could really use one. But he also stops largely because his father's smile has grown beyond amused to downright proud and Jon has no idea why.

"Close your eyes." The Doctor's words are nearly a sigh, but he follows the order without even thinking about it. "Stop thinking so much and just feel. I know you can feel it- that slightly dizzying sensation in the back of your mind, the one you're afraid will throw you off balance if you finally take the time to just look at it." He's right- there is something that he's always noticed hiding in the background but he's never dared to look at. It makes him nervous, scared maybe, and before this moment he's never had even the slightest idea of what it might be.

He still doesn't want to reach out to it, doesn't really know what he'll do with it once it dives out from the shadows and into the light. But he looks anyway.

"What do you see? Feel?"

It rolls over him in one tremendous wave after another. He doesn't even know what it is or how he'd begin to describe it. But the more he looks at it, the more he lets it just crash over him, the softer the feeling becomes, until…

"Calm. Everything feels calm. But…"

There's something else there, another feeling.

"I feel like I'm running. Running in every direction possible- left and right, back and forth, up and down, sideways."

"That's the pull of time. Focus on the calm. That's how you know."

"It just," he opens his eyes, finding his father looking over at him, "feels calm?"

"Yep. Time isn't trying to work and repair itself. It's just enjoying the moment with the rest of us."

"So… if something was wrong, then it would feel…" He searches for a word, the complete polar opposite of calm and comes up with, "stressed?"

The Doctor chuckles a bit at that but nods, "Yeah, something like that."

"And that running- the feeling of being pulled everywhere?"

"The flow of time. Remember the Banitis and how they surround each other? Time pulls on every side, almost equally, just like they push on each other."

"Almost?"

"The Banitis push on all sides equally except- which way are the colours moving? Close your eyes. Where do you want to run to most?"

He takes a deep breath, letting his eyes fall shut, and lets himself run with time. He goes left but then back to the right. He's falling straight down before being pushed back up. Something yanks his shirt, forcing him backwards before he goes forwards again. And- for one brief microsecond- forward is the only direction he's going.

"Forward."

"Forward towards what?"

His brows scrunch together and he's running again. He looks- looks at everything around him. Stares at the place he's trying to run towards, but he doesn't see anything. That's when he stops thinking and stops looking and suddenly, there is it. "Towards… towards that sound."

"What sound?"

"The sound of the TARDIS."

The Doctor smiles at him. "How far away is it?"

"Close by." Jon opens his eyes. "What is it?"

"Where do you think the Time Vortex is?"

Jon's eyes stray back down into the river, studying the Banitis again. They're very close together, touching in spots, but there are still gaps through which he can see the actual flow of water beneath them. "In the spaces between moments?"

"Exactly."

"So that's how you tell? You can hear the boundaries of every moment and tell how close each is?"

"Yep. You'll get used to it. Looking for it. Listening. You just start to know after a while."

He can't help but stare down at the Banitis. They're gorgeous, the pale, pastel colours morphing from one to the next, following seamlessly from one Baniti to the next.

Even though he's not trying to think about it, even though he's just letting the swirling abstract mass of time remain comfortable in the back of his mind, he can still feel it. He can feel the pull of time, the movement of the planet he's standing upon, the utter stillness of the universe for just this moment. It still makes him feel dizzy, makes him just a touch scared, but at the same time, he loves it. For just a moment, he thinks, he lets time surround him, to move to the front of his mind. This time it's not the entire ocean crashing upon him; instead it's fire burning him, power boiling from somewhere deep inside of him, desperate for release.

But his father's hand on his shoulder pulls him away from this and pushes the abstract feeling of time away for now.

"Come on, time to head back in, before your mum wakes up and catches us."

"Right."

He gets up, though reluctantly. He doesn't really notice his father snatching his coat up off the ground or him heading slowly for the TARDIS. His entire focus is back on the swirling sensation of time in the back of his mind and the Banitis before him.

"You coming?"

He tears his eyes away, taking a few jogging steps towards his father. "Yep," he says, even as he looks over his shoulder.