Hi readers!
So, this is a sequel of sorts to Changes: though Changes isn't required reading as there won't be anything major. If you want to read it though, I won't stop you!
All you need to know (Not major story-spoilers for Changes): Hogwarts exists in the real world, and the Doctor saved it before in the first year. Only Dumbledore remembers, because he went into the TARDIS at the Doctor's request, to go meet Amy and Rory (who didn't go to Hogwarts the first time), and the temporal effects of the TARDIS (think wibbly-wobbly-time-wimey) allowed the headmaster to remember. More or less.
Whew... hopefully that made sense to the people who just want to read this.
Oh, and Dumbledore's read the books.

In any case, now that's out the way... This is another Doctor Who/Harry Potter crossover. Something strange is once again happening at Hogwarts...fairly mysterious.
If you squint, you can probably see Harry/Draco for the pairings: nothing too explicit though as they're just in their second year.
If you keep squinting, you can probably find Doctor/Dumbledore. It's not meant to be much more than a close friendship, but their relationship fascinated me while I wrote this.
This is also meant to be running, roughly, along canon. Roughly. Though there may be deviations.

Wow...this is one long Author's Note...
In any case, one more thing to say: please review if you're enjoying! I don't think this is my best beginning, but oh well. Also, I'm considering a Doctor Who adventure like this for each year at Hogwarts. Let me know what you think.
This is for the 11th Doctor.

Enjoy!

The TARDIS made a familiar groaning, wheezing, as it landed.

"Earth!" the Doctor shouted, "2011! Sunny holiday for you!"

"Please say this isn't a honeymoon," Rory replied, "You know how they turn out."

"Nah, this is fun! Exciting!"

The Doctor grinned, barrelling up to the TARDIS doors and swinging them open.

It wasn't quite as sunny as he'd hoped. There was no snow, no rain. Just, no anything. The only light came from the distant stars, the moon was unseen; the warmth of the TARDIS was the only thing keeping him alive.

Swaying in the doorway, the Time Lord stared out. Earth was lifeless. A sheen of ice covered the ground, moisture in the air having turned to solid, and the sky was bare: no clouds, no moon, no Sun. Just stars, distant, watchful.

"And, maybe not," the Doctor finished, swinging the doors shut and darting up to the TARDIS console. "Tracing event to its source…"

"Doctor," Rory spoke up, "I don't understand."

"Oh, shut up Rory, all the things you don't understand could take a while to-"

"Oy!" Amy interrupted, "That's my husband you're talking to!"

"Oh, alright," the Doctor shrugged, fiddling with the console. "Some points in time are fixed. Evidently, this isn't one of them: someone's changed time, coming from…"

He struck a button with a flourish. A few seconds later, he slumped.

"Why, what is it?" Amy frowned, running up and peering at the console screen.

"Hogwarts," she said, loudly, happy. "Now we get to go to Hogwarts!"

O

The barrier to Platform Nine and Three-Quarters hadn't let them through. It was a pain, a real pain, though in retrospect, maybe this wasn't the best idea.

Harry took another look, sideways out of the window.

Yeah, this definitely wasn't the best idea. Instead of taking the train, Harry had accepted Ron's offer; now he was in the pale blue car, flying dangerously high over the spectacular fields, soaring to Hogwarts.

"Can't be much further, can it?" Ron muttered to himself, tentatively patting the wheel.

Harry nodded absently, staring out the window. He was sure he could see…

An unhealthy whine came from the car's engine. The black haired boy looked nervously at the driving Ron. "It's probably just tired," the boy with messy red hair replied, unconvinced.

Harry looked back out the window; sure, they were above clouds, but he could make out something below the white wisps. Dark green backdrop-a forest?-but in the middle, there was something odd. Grey, a little taller… He strained his eyes, glasses almost falling off his ears.

"Not far," Ron murmured, tentatively dipping below the clouds again.

"There!" Harry suddenly shouted, distracted, as he recognized the dramatic landmark of Hogwarts castle. By his ear, the snowy Hedwig cawed.

Ron muttered to himself, egging the car on, as Harry tried to distract himself. He looked back out the window, to see if he could glimpse the irregularity again, but found that the car had flown on too far, and the grey spot in the forest, the Forbidden Forest come to think of it, was long since out of sight.

The blue car flew onwards.

O

"Whoever said you stood out?" the Doctor crooned softly, stroking the TARDIS door.

The blue box stood slap-bang in the middle of the hallway. The hallway leading down to the dungeons, no less; a very commonly used one.

"I did," Amy rolled her eyes, interrupting, "Doctor, can we please move it somewhere else?"

"No," the Doctor crossed his arms, "I like it here."

Amy raised her eyebrows, staring at him.

"Did you break anything?" the redhead said

"No!" the Doctor shook his head violently, appalled she could even suggest such a thing. A second later: "Alright, maybe a little. Forgot normal tech doesn't work here. She's fine, but needs a little while to adapt."

"We don't have a little while," Amy spoke, frustrated as she normally ended up being with the Doctor.

"We do have a little while!" the Doctor protested, "Just a littler while than the little while we need."

"Well, what are we going to do for that littler while?"

The Doctor shrugged. "Improvise!"

Rory groaned. Mr Pond was about to say something, when voice cut through into their conversation; not the huge crowd of students, just muffled groans of complaints of two, and a nasal third voice. Too muffled to hear properly.

Quickly, the Doctor had run up the corridor. Tired, Rory and Amy followed.

As they moved to the outer stairwell, they saw two boys, Harry and Ron, being dragged by the collar, by the tall, pale, sallow Professor Snape.

"And who are you?" Snape sneered, looking the trio of time travellers up and down.

Amy looked at the two students, appraisingly. ""HE does look a lot like Daniel Radcliffe, huh?" she murmured over to Rory

"I don't understand this," her husband replied, frowning

"Me neither," she shrugged. She paused for a few seconds. "Think he looks anything like Daniel did in Equus?"

"We're just passing through," the Doctor hastily spoke to Snape, "Going to see Dumbledore. Oh," he turned back to Amy, "Yes, he does. Or will, I never got the hang of tenses. Never needed them."

"How would you know?" Amy blinked, facing the Time Lord

"I had a friend called Jack," the Doctor shrugged, "Don't ask." He span around back to Snape. "So, what can we do for you?"

"You could get out the way," Snape's dark eyes were locked on the Doctor's.

Harry and Ron looked at each other, shrugging. Above them, the Time Lord and teacher stared at each other. Rory and Amy looked bemused.

"Severus!" a wise, old voice called. A man and a woman hurried down the stairs; in jade robes, Minerva McGonagall was the first to reach the floor, and stop next to Severus. Following her was Albus Dumbledore; the one who had spoken.

Upon seeing the Doctor, the Headmaster of Hogwarts, for a brief second, appeared almost afraid. He knew what the Doctor's appearance heralded.

"I believe the students are in your House, Minerva," the bearded wizard nodded to the witch at his side, "Do what you see fit."

Harry and Ron exchanged frightened glances.

"And Doctor," Dumbledore looked at the Time Lord, "Amy and Rory. I believe we must talk."

As Minerva and Severus spoke to one another, above the nervous pair of students, the Headmaster of Hogwarts lead the trio of travellers away. They went down the corridor, until they stood next to the comforting blue figure of the TARDIS.

"Why have you returned?" Dumbledore looked at each of them

"Ah, yes, Albus, that could take a while to explain," the Doctor dithered on the spot, "Well, we landed a little way in the future, then hopped back `cos things were going really, really badly, traced things to Hogwarts and Bam!" he slapped his hands together, "We're here, right?"

"I don't think anyone understands what he's babbling on about," Amy stage-whispered to Dumbledore. The teacher smiled.

"I know the feeling," Dumbledore spoke. "I trust you're not here for employment once again, for I feel I must inform you the job has been taken by a Gilderoy Lockhart."

Amy groaned: "Never liked him."

"Don't say that!" Rory quickly interjected, "Spoilers, as he always says."

"Do not worry Mr Williams," Dumbledore said kindly

"Pond," the Doctor interrupted, "He's Mr Pond."

Rory shrugged at the headmaster.

"Do not worry, Mr Pond," Dumbledore's eyes were twinkling, "I have read the books, I know what to expect."

Rory scratched his head, deciding not to even try and understand.

"Ah, right," the Doctor nodded, "Reminds me, why did you come down here? In the book, Snape went away to call you, you didn't come down by yourself."

"I was investigating the centaurs."

"Centaurs?" Amy raised her eyebrows, "The hot horse-guys?"

"Those who reside in the Forest, yes. People have said one has been wandering the streets of Hogwarts during the feast."

"Alright then," the Doctor clapped his hands, "That's why we're here then!"

"Really?" Dumbledore sighed wearily

"No, well, yes, well, might be. Never know, could be connected! Now, the question is, what'll we call ourselves…" the Doctor trailed off, seemingly thinking about that more than he was about the fact the Earth was frozen in a few years time.

"I want to be Scully!" Amy chirped

"Right then," the Doctor puffed himself up, "I'm Mulder."

"Mm, Foxy," Amy and the Doctor laughed at her pun, before Rory butted in;

"You do realize no one here knows who we are, right?"

"Oh, alright," the Doctor slumped, "Party-pooper. Be boring like that then."

The TARDIS sparked into life beside them, a little light emanating from the upper bulb, and the windows illuminating again. She'd recovered from the sudden shock of landing.

"Back in a sec!" the Doctor announced, ducking into the TARDIS.

About five seconds later, he was running back down the staircase, past Snape, Minerva, Harry and Ron, to his companions and Dumbledore. "Just parked her in your office, hope you don't mind," he grinned, "Probably couldn't do much about it if you did actually, sorry.

O

"Doctor," Rory called.

They'd been here a day so far. They spent the night in the TARDIS, using the maze of rooms inside it for housing. Rory had suppressed his questions for that day, but after the night, they were overflowing.

"Yes Rory?" the Doctor stepped out of his wardrobe.

The Time Lord turned around, blinking. "So that's where that door goes." Grinning at his latest discovery, he turned back to Rory: "Where's Amy?"

"Gone out to Hogwarts," he shrugged, "We're 'investigators' now, Dumbledore said."

"Really?" the Doctor plonked himself down on a chair opposite Rory, "I miss the days where I was just a meddler."

"Doctor?"

"Yes Rory," the Time Lord repeated himself with a groan

"How does all this work? I mean, Harry Potter's just a book, right?"

"Nah, that'd be no fun," the Doctor shook his head, "There are loads of stories taking place on Earth right now, all in parallel. Not like parallel universes, but more…playgrounds. I like playgrounds. Just a skip away from each other, but the people actually in the playgrounds never bother to cross over: they can't. Wizards have a spell for it actually; that one they've got to repel Muggles, it works the same way, stopping any of the none-wizards hopping through. Of course, doesn't work for us. Time travellers; we can hop through the playgrounds. Of course, aliens can too, they don't come from Earth to the earthly playgrounds are the same to them. Get it?"

"Um…I think," Rory frowned

"Good, you can explain it to em," the Doctor was about to continue, when they heard the phone ring.

The Doctor got up hastily, running out of one of the two doors (excluding the wardrobe) which lead to the Ponds' room. There was a splash. A few seconds later, a soaking Doctor re-entered the room.

"That's where the swimming pool ended up," he grinned, before leaving, at a run, through the other door.

About thirty seconds later, he barged out of the wardrobe again, past a surprised Rory. The Time Lord stopped, looking around, eventually realizing he'd been there before.

"You moved," he moved very close to Rory, pointing a finger accusingly

"Uh…no," Rory murmured, bemused. "Don't you know your way around your own time machine?"

"No fun that way," the Doctor shrugged, "Besides, things are always shuffling around. Dimensions are a little off balance, bigger on the inside, and I can never remember where the button to turn off the shuffle is."

"There's a shuffle?" Rory blinked

"Yeah. Well, technically it's hide-and-seek mode. But 'shuffle' sounds better."

The Doctor paused, looking around before, with a triumphant expression, opening a drawer from the bronze wall and, somehow, hopping all the way inside it.

Rory walked over to the drawer, eventually realizing the noise of the ringing phone was emanating from it. He peered down into it; the TARDIS control room was within.

Mr Pond rolled his eyes; he'd put the Harry Potter books in there, for suitable reading. Now he'd never get them back: who knew which bit of the TARDIS they'd ended up?

Curious, Rory listened to the Doctor as he babbled into the phone:

"Yes, Marilyn, I said I'd be back in a- oh, hi Amy. What? …Right, be there soon." He slammed the phone down. "C'mon Rory!" he called.

After several minutes of wandering through several rooms, including a library, an ecosystem full of butterflies, an empty plaza, and tennis courts which looked like they were made out of cheese, Rory found his way to the console room. By the time he got there, the Doctor was already in his coat, and was tapping his foot on the grating.

They left the TARDIS, into Dumbledore's office, almost immediately.

O

"I think that counts as something suspicious," Amy muttered, pointing to the floor.

They were on the second floor. The ground was made out of the normal grey, impassive stone; covered in a thin spread of water. Most likely because of their proximity to Moaning Myrtle's bathroom.

None of that was important though; it was all common place. One other thing though had caught Amy's attention.

Damp, right in the middle of the floor, there was a small, black book. Its pages were yellowed with age. Evidently, it had rested there a while, as water was seeping through its pages.

The Doctor knew, if he knelt down and picked it up, it would be easy to find a few words written neatly on it: Tom Riddle's Diary.

Straight through the centre, there were two, great gaping holes, gaps in the pages and cover. Black stained the pages, and ink trickled out over the ravaged edges of the gaps, looking eerily like blood.

The Doctor walked up to the Diary, and simply flipped it over. "Dead," he intoned dully; "Bitten, judging by the tooth-marks."

"Is that really all that bad?" Rory frowned, feeling he was missing something.

"You need to read the books more Pond," the Doctor looked up with a flippancy he didn't feel in his voice, "Mr Pond, not you Amy," he amended, "This isn't just a diary," he dropped the book, "It can't be destroyed that easily. Basilisk venom would do it though; and guess what it looks like bit it."

"But…the Basilisk was under its control, right?" Amy frowned

The Doctor looked at the lifeless Diary, and then at the redhead. "I thought so too."