It was all Sirius Black's fault.

Despite the fact he'd known Harry was coming to stay at 12 Grimmauld Place for Christmas, he'd just had to go outside in the rain as Snuffles and catch what Madam Pomfrey said was Animagus Flu. So, despite the fact that Harry wasn't an animagus - yet - barely a day into the holidays, here he was back at Hogwarts.

Currently, Harry Potter was wandering through the deserted corridors, kicking bad-temperedly at the plinths of the statues he passed. Hermione had gone to spend the holidays with her parents, and the Weasleys had gone to visit Mrs Weasley's Great-Aunt Muriel. According to Dumbledore, Harry would have been sent to the Dursleys, but it seemed they'd gone on holiday as well. Really, Harry thought, as if anyone would believe the Dursleys had actually gone to Madagascar!

He didn't understand why he couldn't have stayed at Grimmauld Place. Okay, so Sirius was sick, but Harry wasn't an animagus. Remus and Sirius had been teaching him the theory, but they hadn't really gotten very far. So he would have been safe, and having fun, instead of stuck in this cold, damp, dusty castle . . .

Harry's thoughts ground to a halt as he was ambushed by a giant sneeze. Caught off balance, his shoulder rubbed against a tapestry on the wall beside him, one that had obviously been missed by the house-elves when cleaning, as a choking cloud of dust rose from it. Harry sneezed another four times in quick succession, and then had to close his eyes as he was struck by an overwhelming sense of vertigo.

When he finally felt steady again, he opened his eyes . . . and startled.

His vision had changed. It seemed to narrow and stretch, with a blank spot dead ahead of him. Oddly, though, he could see the walls on either side of himself more clearly than he'd ever seen them in his peripheral vision. And he seemed to be breathing differently, too.

Tentatively, Harry went to raise a hand to his face to feel what had happened, but as he moved it, his sense of balance shifted and he nearly fell over.  Confused, he lowered his hand again, and looked down to see what the problem was. Once he'd tilted his head to bring his lower body into focus, he startled backwards and let out a shrill cry of alarm. He'd turned into a black skeleton!

Well, it should have been a cry of alarm, but what actually came out of his mouth was a high-pitched call that sounded vaguely equine.

Harry closed his eyes again. It's just a nightmare, he told himself. You slipped and bumped your head when you sneezed, and now you're dreaming. Wake up, Potter!

Unfortunately, when he opened his eyes, nothing had changed. His heart sinking, Harry looked down at himself again. He wasn't actually a black skeleton, he realised, but just a very skinny, black-coated . . . horse? Something rustled behind him, and when he tilted his head to see - not that he had to tilt it very far - he realised it was wings. His wings, to be precise. Long, black, leathery wings that seemed to be attached to his shoulder blades. A thin, dry-haired tail swished behind his rump.

Oh, Merlin, Harry thought. I'm a Thestral!

Desperately, he squeezed his eyes tightly shut and tried to force himself to sneeze again. Don't let me be stuck like this. I don't want to be a Thestral!

Something suddenly smacked into his rump, and there was a muttered curse. "What in Merlin's white beard . . . ?" Harry turned his head to look.

Snape! He'd be able to help, Harry was sure. But . . . could Snape see Thestrals? A surge of panic rushed through Harry, and he found  himself tossing his head back and opening his wings. Snape hurriedly skipped back a step. But was it because he could see what Harry was doing, or did he just feel the movement of Harry's wings? A further rush of panic caused Harry to rear up, as he tried to turn around to face Snape. Unfortunately, he was too large for the corridor he was currently occupying, and ended up banging his head against the stone ceiling. With a pain-filled sound, Harry woozily dropped to all fours again.

"What on earth is a Thestral doing in my dungeons?" Snape wondered out loud. He had folded his arms across his chest and was watching Harry closely. "Just how did Potter get you away from Hagrid and down here?"

Hey! Harry let out an indignant equine huff. It's not my fault. I didn't bring this thing down here . . . I mean, yes, I did, because it's me, but it wasn't on purpose! He aimed a desultory kick at Snape, and was pleased when it made the professor hastily skip back another step. The sound of his hoof clopping as he placed it back on the ground, however, reminded him that if he ran the professor off, he'd very likely be stuck like this for a very long time. Harry lowered his head and tilted it to eye the professor, uttering a plaintive neigh.

Severus Snape rolled his eyes. "Of all the blasted luck . . ." he muttered. He turned away, then paused when the Thestral let out a panic-stricken call. "Shush, you idiot creature," he snapped. "I'll get you out of the castle, but I need something to lead you with."

Harry shuffled his hooves as Snape disappeared further into the dungeons. Which way was out? Harry wondered. Behind him, he thought. Deciding he could at least get himself ready for when Snape came back, he attempted to turn himself around. Unfortunately, Harry hadn't taken into account just how long his Thestral body was, and in short order he found himself jammed cross-wise across the corridor, his nose pressed almost into his chest, and his rump squashed against the opposite wall.

"Merlin!" The startled exclamation made Harry roll an eye. Snape had returned, and had stopped dead in the middle of the corridor, a rope trailing from one hand and a thick chunk of raw meat held in the other hand. Snape's mouth twitched . . . once, twice, a third time . . . and then Snape was collapsed against the corridor wall, laughing hysterically.

Harry rolled his eyes, snorted, and then gave a strident neigh that clearly meant "don't just stand there laughing at me, HELP me!"

Finally, Snape pulled himself together and approached the stricken Thestral. Its nostrils flared as it scented the meat he still held. With the rope looped around its neck, Snape gently tugged at one end, as it moved its head to follow the meat, and pushed at the other, until finally it was standing in the middle of the corridor once more, in the opposite direction to where it had started.

When Snape tried to lead him down the corridor and out, though, Harry discovered that it was harder to walk on four legs than he'd ever thought - not that he'd ever given much thought to the matter. When he lifted a foreleg to take a step, he almost fell over. Snape looked over his shoulder as he felt the tug on the rope, and raised an eyebrow. "Dunderheaded creature," he muttered under his breath, and came back to steady the Thestral.

Harry gave an equine sneeze, and wasn't terribly disappointed that Snape's hair had been in the way. He nickered as Snape glared at him. "Do you want to get out of these dungeons, or not?" he growled. When the Thestral lifted a front leg to take a step and nearly fell over again, Snape shook his head, and absently wondered if Thestrals could get drunk.

It took almost half an hour for Snape to lead Harry out of the castle, with Harry tottering as though he had no bones in his front legs and resting his large head on Snape's shoulder for balance. Once outside, though, Harry ran into another problem. Snape had led him to where a medium-sized herd of Thestrals were grazing in a pen just beside the Forbidden Forest, put him in the pen, and then returned to the castle. All Harry could do was watch his only hope of salvation walk away, as no amount of high-pitched calling made Snape even look back.

Snuffling noises behind him made Harry freeze. Ever so slowly, he tilted his head to look back. The Thestral herd had come to investigate their newest member. The lead stallion was sniffing at Harry. Harry let out a squeal, as the stallion's nose went places that no-one except Harry had ever touched, and instinctively kicked out. The stallion backed away with a sound suspiciously like laughter.

Harry spent the next three days pressed deep into a corner of the fence, his tail clamped tightly against his hindquarters. He was going to kill Snape when he changed back!

Two days later found Harry - thankfully human again - sitting on the bottom of the main staircase in the Entrance Hall. He didn't seem to have any side-effects from his time as a Thestral, but he had been craving rawer meat than he usually did.

His Potions textbook was next to him on the stairs, but rather than actually reading through it in preparation for completing Snape's holiday essay - as if the greasy bat expected anyone to complete homework over the Christmas holidays! - Harry was using it as a support while he wrote to Sirius and Remus. If Sirius got better really soon - like in the next day or so - then maybe Harry could actually have fun for the rest of his holiday.

Once he'd finished the letter, Harry went to pull open the large doors leading out of the castle and called for Hedwig. He lounged in the doorway, soaking up the little sun there was, while he waited for her.

A sudden strong breeze, carrying a few flakes of snow, blew straight at him, and caught him full in the face. Harry spluttered, and then felt an ominous tickle in his nose. Oh, no! A gigantic sneeze almost had Harry off his feet. He collapsed back against the open door, and half-fell, half-rolled onto the Entrance Hall floor.

Unfortunately, it seemed Filch hadn't gotten around to cleaning that part of the castle yet that day, or even that week, as the floor was covered in a half inch of dust. Harry scrambled onto his hands and knees, his eyes streaming tears as he tried to stifle the desperate urge to sneeze.

Half a dozen forceful sneezes later, Harry felt the same wave of vertigo wash over him. When it finally passed, he resignedly opened his eyes and looked down, expecting to see the familiar skeletal black legs.

What he actually saw, however, were golden, scaly legs with three large, sharp talons on each foot.

What . . . ? Harry turned his head, and realised that his vision wasn't the same narrow, sideways view the Thestral had had, but was more front-facing like his human vision. But the detail . . . It felt like he could see every individual speck of dust on the floor. This made it incredibly easy to see that his rear end was indeed black and horse-like, and he still had wings, but from his shoulders up it changed to glossy black feathers.

"Oh, for Salazar's sake, not again!" Harry looked round to his left, to where Severus Snape was standing at the entrance to the dungeons. "How many times has Dumbledore told Hagrid that creatures larger than Fang belong outside the castle? And now a Hippogriff!" Snape shook his head.

Harry blinked. He was a Hippogriff? He thought back to his third year, and Buckbeak. Hippogriffs didn't like arrogance - as Malfoy had proved - and Snape was as arrogant as they came. Oh, yes, this could be fun! Harry thought, and gave an evil chuckle, although it came out as a cross between a horse's neigh and an eagle's screech.

Snape, unfortunately, did not shiver in fear, or flee in terror, but instead rolled his eyes, and moved to stand a good six and a half feet in front of Harry. He paused, then bowed from the waist, lowering his head so that while he wasn't completely lowering his gaze and exposing the vulnerable back of his neck, nor was he meeting the Hippogriff's eyes, which would have been taken as a challenge.

Harry entertained the brief thought of darting forward to attack the Potions professor, and clicked his incredibly sharp yellow beak, but the Hippogriff part of his mind was impressed by Snape's actions, and after a hesitation of his own, Harry found himself bending one leg in a bow.

With an unseen sigh of relief, Snape straightened up and approached the black-and-white Hippogriff. He'd never seen one with so much black before, but this one was solid black from its eagle head to its horse . . . knees, where it tapered into black with white spots. Or was that white with black spots? Ensuring that the beast could see what he was doing, Snape slowly raised a hand and ran it down the Hippogriff's neck, stroking its feathers.

Harry let out an involuntary, pleased chuffing sound, then caught himself. If Hippogriffs had been able, he would have been blushing fiery red. What am I doing? he scolded himself. This is Snape! Mean, nasty Snape! No chuffing when he's stroking you! Oh, Merlin . . . Harry shook his head at his own thought. That had sounded very bad!

"Come along, this way," Snape interrupted his musing, pressing firmly on the Hippogriff's neck to turn its head towards the still open door. "I'm sure you'll be more comfortable outside, where you can stretch your wings."

Gloomily, Harry allowed himself to be . . . persuaded out of the castle. If Snape thought for one second he was going to be put with the rest of the Hippogriffs Hagrid kept, then Snape was going to get a big surprise!

A sudden sharp, shooting pain in his left wing caused Harry to screech in surprise, then he whipped his head around and glared at the Potions professor, who was holding a long black feather in his hand. The man had plucked him! He clicked his beak warningly, daring Snape to try that again.

"My apologies," Snape said, soothingly. "The feather was broken and misaligned, probably from when you went past the door." He held up the feather, showing that the end of the feather was bent and cracked in half. Harry huffed, and turned to run his beak through the feathers on either side of the gap, preening them back into place.

"Ah, Hagrid!" Snape suddenly called, and Harry froze. "It seems one of your Hippogriffs got into the castle." Before Snape could say anything more, and before Hagrid could even open his mouth, Harry was galloping away from them, flapping his wings as hard as he could to get himself off the ground. Perhaps he'd just hide out in the Forbidden Forest until he changed back!

Grumbling to himself, Harry slammed a jar down forcefully onto the shelf in front of him. Snape had caught him sneaking back into the castle after finally changing back from a Hippogriff the night before, and without even pausing to ask Harry what he'd been doing, had given him three nights detention for being out after curfew.

It's not fair! Harry slammed another jar down. It wasn't as if he could have been in the castle before curfew . . . well, okay, he could have been, but as he was still a Hippogriff at the time, he would only have been put outside again.

Dang unfair greasy . . . Harry kicked the bottom shelf, and then watched in horror as a jar full of pixie dust teetered and then fell to the floor, where it smashed into a thousand little pieces. The dust ballooned into the air, and Harry clamped his hands over his nose. Oh, no, please, no! He was too late. Several giant sneezes knocked him off his feet.

It seemed to take an awful long time for him to fall. And he landed on all fours, instead of on his backside as he'd expected. Harry opened his eyes, and then blinked several times just to make sure he had opened them.

If his eyesight as a human was terrible, his eyesight as a . . . whatever-he-was was a lot worse. He appeared to be almost completely blind. He had a very acute sense of smell, though. Harry took a deep breath, and the combined scents of the ingredients caused him to sneeze. Unfortunately, it didn't cause him to turn back as he'd hoped. Harry snuffled at himself, trying to get a sense of what he was this time. He appeared to be an overgrown mole . . .

The door of the storage cupboard suddenly flew open, letting in a flood of light, and a stream of extremely nasty curses. Harry blinked up from his position on his back to see something straight out of his worst nightmares - Severus Snape in a towering rage.

"POTTER!!" Snape bellowed, and even as Harry twisted desperately to right himself and burrow under the shelves, Snape was reaching for him. He found himself tucked firmly under Snape's arm, a hand clasping the back of his neck, as Snape strode for his office door. "When I get my hands on that boy, he'll wish I'd use him for potions ingredients," Snape growled under his breath. Harry cringed. "I knew I should have searched him for that dratted Cloak of his. Letting a Niffler into my stores . . . ! I'll have Potter in detention until next Christmas!"

A Niffler? Was that what he was now? Harry wracked his brain for any knowledge he might have picked up about Nifflers. Hadn't Hagrid done a lesson on them once? They liked . . . Harry's nose twitched . . . they liked . . . what was that delicious smell?

With a sudden lunge that took Snape off-guard, Harry tried to dive towards the enticing scent. Unfortunately for him, Snape still had the hand at his neck, so all Harry managed was to nearly hang himself as Snape's grip tightened.

"Oh, no, you don't!" Snape said, sharply, bringing his handful up so that he could meet the Niffler's gaze. "You are not getting anywhere near my gold cauldrons! Not unless you want to be part of a potion brewed in them, anyway." Harry sneezed in reply, then went completely limp when Snape tightened his grip in warning and narrowed his eyes.

Still muttering to himself, Snape tucked the black, furry Niffler back under his arm and headed out of the castle towards Hagrid's hut. He'd know what to do with the pesky little blighter.

A week later, Harry finally seemed to have stopped turning into random creatures. Just in time to welcome everyone else back from their holidays.

He was standing with Ron and Hermione in the Great Hall, when a commotion at the doors attracted their attention.

"Harry, watch out!"

Harry turned just in time to see a large black furry something streaking at him. The next moment, he found himself flat on his back on the floor, with what looked like a cross between a ferret and a rabbit - a very large cross between a ferret and a rabbit - perched on his chest and growling into his face.

"Ugh!" Harry said, turning his head away from the foul breath emanating from the . . . thing. "What . . . ?"

"It's a jarvey!" exclaimed Ron. "But what's it doing here?"

"Stupid Potter!" the jarvey growled, and snapped its over-large front teeth millimetres from Harry's nose. "Your fault!"

"Umm . . ." was Harry's eloquent response.

"Don't hurt him!" Professor McGonagall's voice sounded from the Hall entrance. "It's Professor Snape!"

Snape?! Harry looked back at the incredibly angry creature on top of him, and suddenly recalled each and every time he had sneezed on Snape whilst as various creatures. Oh, Merlin, no . . .

"Potter potions," the jarvey crooned, its front feet kneeding at Harry's chest. "Yucky stuff, Potter!"

Before Harry could even begin trying to work out what Snape was saying - was he threatening to turn Harry into potions? Giving him a detention? - the jarvey sneezed violently, then closed its eyes tightly as if dizzy. Oh, no . . . !

But before Harry could shout for help, or even get out of the way, there was a small pop! and in the jarvey's place was a small, long-feathered Fwooper bird, glaring evilly at Harry.

Harry gulped. He was really in for it now! The Fwooper had bright pink feathers.