Summary: A new threat against Camelot has arisen, and Arthur is determined to find out what it is. Merlin thinks he has the perfect plan-to infiltrate their enemy's ranks. And who would suspect an innocent cat? Unfortunately, Merlin needs a bit more practice with his shape-shifting magic...

Warning: Takes place following Season 4, episode 2, but I'll try not to have glaring spoilers for anyone.

Words: 3,000-ish.

Notes: You have no idea how much fun it is to write this story! Here's hoping its equally as fun to read.

The name is inspired in part by the always amusing poem/song:

The cat came back the very next day,
the cat came back—thought he was a goner,
But the cat came back for it just wouldn't stay away.

It's very fitting, I promise.

The Cat Came Back

Chapter One: Catcall

The table shook when Merlin slammed his head down. He didn't dare open his eyes and face the window.

Instead, he liked to pretend that the stars were still out and his back wasn't warm because of an early sunbeam. He liked to pretend that he hadn't been trying the same spell for over six hours with as much success as a fire underwater.

At this point, he didn't even care if Gaius woke up and lectured him.

But the snoring roared on and Merlin's back remained warm.

He sighed out his exhaustion and sternly told the wood of the table, "It is going to work."

Cloth shifted as Gaius turned over.

With his eyes closed and his mind so tired it was blank, he repeated the spell. He could feel his magic coursing through his veins, trying to reach every part of his body. It felt so natural to have it flowing freely so for once, he just let it be. He didn't try to hide it or stifle it.

It was like taking a full breath for the first time in years.

But the magic faded, and he could once again feel the warmth on his back. His whole body slumped in disappointment.

'I'll have to try again when Arthur's done with me.'

He might have continued to slump over the table as the picture of misery, but the smell of food drifted past him. It took him by surprise, and he opened his eyes.

He promptly fell off the chair in his shock.

'Gaius! I think I ruined the world.' Merlin was sure he meant to say the words out loud, but the only thing he heard was an undignified whine.

He tried to put a hand to his throat, as if that would tell him what was wrong, but something felt unnatural. He looked down. There, in much sharper detail than he should be able to see, and slightly distorted colour, was a cat's paw.

Merlin stared at it a little longer.

He flexed his hand, and the paw flexed too. He stretched a little father, and felt his fingers dig into the ground as claws extended from the paw.

A gleam came to bright blue eyes.

It worked.

'Never mind, Gaius, I fixed it,' he tried to say, but again he only heard a soft mewl.

He grinned.

This time, when he looked around the room, he understood. Things weren't bigger and the world didn't lose its crisp colours because he'd ruined it, but because he was looking through a different set of eyes.

After a sleepless night of practicing in the dark with whispered words and no progress, his shape-shifting magic worked.

He flexed his new claws experimentally. He turned his head to catch sight of a fluffy, almost black tail. It twitched, quite against his will. He tried to flick it to the right, but it went left. He told it to lie flat, but it swished back and forth.

'Oh well. Who needs a tail anyway?'

He sniffed the air. The tempting smell of cheese and bread was drifting on the slightest of breezes. It was what had roused him earlier. Merlin was sure that Gaius had not left his breakfast out, which meant that Merlin could smell food through the cupboard.

He flicked his ears forward and back, and marvelled at the different sounds they picked up. Forward, and there was the wind whispering through the corridors and making the wood creak. Back, and Gaius' snores were like thunder. There was a scuffling sound to his right, and footsteps to his left. Servants starting their mornings with the rising of the sun.

His cat-grin widened.

'This is perfect!' he thought. He took a step toward the cupboard that had such tempting smells-

Only to stumble over his own paws and go headfirst into the table, sending his stack of books clattering to the ground and nearly on his head. All because he forgot to pull in his front claws before walking.

The noise made his ears wring, so he wasn't surprised to see Gaius startled awake and sitting up. He was looking around wildly, never toward the ground where Merlin picked himself up, shook out the dust in his fur, and sat down as if he owned the world.

It was quite hilarious, but after five minutes of watching Gaius look confused, Merlin grew bored. He decided it was time to get Gaius' attention, so he meowed in his most demanding voice, as he'd seen other cats do when they want something.

What came out was a high-pitched squeak.

Gaius finally turned toward him. His frown deepened. "A black cat," he said. His tone was wary in a way that Merlin didn't expect.

Merlin looked himself over and tried to find what it was about his new body that was so suspicious.

"More of a kitten, really."

Merlin froze.

A kitten?

A tiny, defenceless, pathetic kitten?

He scrambled toward the stairs, forgetting once again that extended claws had a tendency to dig into wood. After tripping and rolling back to his feet, he was faced with a climb that looked nearly impossible. His head hardly cleared the first step. But with determination and claws that could finally serve a better purpose than tripping him, he made it up to his room.

To his fortune, he'd not cleaned said room properly in weeks, which meant there was all manner of things scattered across the floor. In particular, there was a shiny food platter he'd stolen from Arthur when the prat had been staring at his reflection for too long. Now Merlin stood over this make-shift mirror and stared into the wide, innocent eyes that were staring back.

'Why?' he asked the universe.

With his heightened senses came a trade-off: the world was now in muted colours. It was not that he couldn't tell what each colour was—his fur was a dark brown that would be black if it weren't for the sunbeams sifting through it, and his shirt in the corner was a deep red—but they were not as vibrant as he was used to. Instead, their edges were crisp and clear, and any slight movement, like the wind rustling the leg of his pants, stood out in sharp detail.

But even when the world's colours were dulled, the eyes staring up at him were the exact shade of blue as they'd been when he was human.

He looked over his reflection mournfully. Indeed, his face was not sharp and defined, but round. His eyes were large. His ears were large. His body was covered in medium-length fur that was sure to keep him warm in the coming winter, but was a touch too fuzzy to belong to a dignified, respectable older cat.

His whole body slumped—he'd turned himself into what looked like a six-month-old kitten.

He was still staring at himself miserably—moping, Gaius would have said—when he heard footsteps that were almost booming coming up the stairs.

He looked up. Then looked up some more. Then he was finally looking up far enough that he could glare at Gaius.

The old man's brows furrowed. Merlin watched as Gaius took in the bed, neatly made and clearly lacking a young boy. Gaius looked back at a cat that acted a little too human, staring into a mirror and now glaring. Then he must have noticed the eyes that were as open and expressive as they'd been when he was human, because Gaius knelt down.

"Merlin?"

Merlin forgot about his young appearance in favour of beaming with pride. It was clear in his catty smirk, and in the way his tail was straight up in the air (he told it to go back down, but it continued to do what it pleased). He sauntered over to Gaius, with his claws carefully sheathed.

"What on Earth have you done now?"

Merlin had his mouth open and ready to retort before he realized that despite his most careful effort, he would not be able to form words.

'I should have worked out a spell to make cats speak,' he thought ruefully.

He held out a paw and slid his claws out, intent on scratching his answer in the wood of the floor.

He was whacked upside the head, and though it was half the force as normal, his world still trembled for a moment.

"Do not wreck my floors with suspicious messages like 'I was being a fool again and practicing obvious magic.'"

Merlin scowled.

"You might as well change yourself back and tell me," Gaius said.

Merlin rolled his eyes—an act he was glad he could do even as a cat. All of his hard work and Gaius couldn't even see the brilliance.

No matter. He was confident that he could pull it off again now that he got the hang of it. And it would be awfully nice to have the world back to its proper size, where bed posts didn't loom over him like trees, and where he didn't trip himself just trying to walk (...or at least where he didn't trip himself as often...).

He was about to recite the ever-essential "undo" spell when a horrible realization dawned on him.

'I can't talk.'

He tried anyway, wincing at the series of mewls and howls that came from his throat, but he didn't even feel a stirring of his magic. He tried to think it, very forcefully, but there wasn't a flicker.

In a panic, he stared at the red shirt across the room and willed it to move, as he'd been doing since birth.

Finally, the magic bubbled up inside of him and the shirt rose off the ground. It wobbled mid-air and dragged the sleeves as it drifted toward him. His paw didn't make a very good conduit the way his outstretched hand had as a human, but at least he could breathe, in the only way he'd ever known. He didn't want to imagine what life would be like if his magic was cut out of him.

He let the shirt drop and felt an odd tiredness sink into his bones.

He turned worried blue eyes up at Gaius, begging for understanding.

Gaius' gaze softened, and he put a large hand over the whole of Merlin's head. "Never mind. I'm sure we'll find a way to fix this before Arthur leaves tomorrow."

Merlin closed his eyes and leaned into the touch.

The world was too loud, now. He could hear the pulse in Gaius' hand as clear as the wind whistling through castle windows. He could catch snippets of voices as they passed their quarters, and if he flicked his ears toward them, he could sometimes catch words.

Yes, a cat was a perfect spying disguise, but what use would he be with nothing more than instinctual magic if he couldn't make himself human again?

oOoOoOo

Their morning passed in stifling silence—a sure sign that the world was not right if Merlin was in the room.

Said warlock-turned-feline glanced up (and didn't that feel weird, having to look up when he was standing on a table?). He searched Gaius' face for any sign of success, but there was none. Only the strain of frustration.

Merlin went back to work. His right paw was sticky with ink. He used the tip of his claw as if it were a quill and practiced his cat-calligraphy. It was more difficult than he'd anticipated. His arm didn't have the same range of motion that it used to, so he often had to use a well aimed flick of the wrist, which was as likely to produce the desired effect as it was to produce a giant ink blob. After three hours, his writing could almost pass as "human".

There was a heavy thunk as Gaius closed his book. "I'm afraid there is nothing in my books that can change you back," he said. Merlin let his paw rest and hesitantly looked up at Gaius. "The spell you used was meant as a curse, to turn someone else into an animal. Only you can reverse the effects."

'And I can't talk,' Merlin concluded.

Gaius frowned at the resigned mew.

Merlin focused on his paw, and the ink that was currently making little pools of black all over his hard work. With painstaking effort, he traced letters onto the unmarred corner of the parchment. He controlled his muscles and made tiny, delicate movements, until there were legible words.

Merlin felt a warm breath ruffle the fur on the back of his neck as Gaius leaned over to read what he'd written.

Checking the library may take days.

Gaius' sigh made Merlin squirm. "I'm sorry, Merlin. I'll tell Arthur that you're unwell."

Merlin's head whipped up and he fixed Gaius with a glare that could make even a full-grown male cat tremble.

'I am not staying behind!' was the message that was clear in his bright blue eyes.

"Arthur will be fine," Gaius continued, "He's only going to be there long enough to gather information and get an estimate of their numbers."

In a hasty scribble, Merlin wrote, That's why I need to go.

"You're a kitten, and a suspicious looking one at that. It's far too dangerous." Merlin would have responded, but Gaius grabbed his paw. "I'm serious. You can hardly use magic."

Merlin wrenched his paw away and scrambled to the other side of the table, where he wrote, in messy cat-ligraphy that showed nothing of the grace he had practiced, In this body, I can do more than estimate their numbers.

Then he bounded off the table and focused all of his instinctual magic toward opening the door.

"Merlin!"

He didn't know if Gaius sounded so outraged that Merlin had run away, or if it was because he'd written right on the wood of the table for anyone to see. Merlin didn't stick around to find out.

The door slammed shut behind him.

As he caught his breath, Merlin began to realize how much trouble he was in.

He'd thought he gotten used to the world in the last three hours. He hardly ever tripped over his own front paws, and he was beginning to identify where every smell and sound was coming from.

Now, the world smacked him in the face. There were so many new scents, like the grass and the flowers and the food in the kitchen, and a thousand other things he'd never smelled before. He could hear birds, and rustling, and shuffling, coming closer and closer.

He let out an indignant howl as he was body-checked and sent flying. He landed on his feet, but then went stumbling head over paws.

His world went dark.

He panicked, clawing at the net that was pinning him to the ground. He thrashed and rolled and tried to get the smell of the river out of his head, until suddenly, there was light, and he could breath fresh air again.

He looked down.

His head was sticking out of the sleeve of a shirt.

(Merlin was glad that a cat couldn't flush in embarrassment)

"You wretched creature!"

Merlin followed the voice up to the seething servant that he'd accidentally tripped. The man was red-faced and clearly not a friend of innocent kittens, judging by the way he now loomed over Merlin with the blood-lust of a starving wyvern.

"I'll have to do the wash all over again! Sir Gwaine will never let me hear the end of it if I tell him a stupid animal is to blame."

Merlin was on the brink of feeling sympathy for any servant who was stuck with Gwaine, until he heard the word "stupid".

A new sort of glint came into bright blue cat eyes.

He not-so-subtly turned to stare at the trail of inky paw prints that followed him out of the physician's quarters, then raised his right paw.

The colour drained from the servant's face. "I swear, if you so much as-"

With a cat smirk, Merlin pressed his paw down, leaving a very distinctive ink stain. Then, while the servant's anger consumed him, Merlin stomped all over the shirt until it was covered in dirt and ink.

Merlin, remembering that he had to be alive if he was to be of any use to Arthur, scrambled out of the shirt and ran straight through the servant's legs.

"I'll kill you!"

The laundry was forgotten in favour of a mad chase.

'That's not very responsible of him,' Merlin thought. (Never mind that he'd left Arthur's clothes in the kitchen more than once in favour of sneaking out a few extra fresh-baked bread rolls)

He ran faster.

It might have been adrenaline or survival instinct, but he could feel a strange strength in his back legs, propelling him so fast that the doors in the corridor began to blend together. His sharp sight kept track only of what was in front of him, like the girl carrying a tray of breakfast, and the mouse who saw him coming and darted back to a hole that Merlin had never known was there.

He raced down flights of stairs without so much as a stumble, and zipped past two guards completely unnoticed.

'Arthur would never catch me like this!'

No sooner had the arrogant thought crossed his mind that he rounded a corner and snagged his back claw on an unsuspecting royal red carpet. He went sailing through the air and tumbled forward like a ball of extra-fuzzy yarn. His world was spinning and his head rang, so he didn't bother trying to process the whole new set of sights and scents and sounds.

He laid still.

"Despite five witnesses, you still claim that you have no magic?"

Merlin felt his blood run cold.

A/N: That's it for a first chapter! If you have any unfulfilled dreams of what Merlin would do if he were a cat, feel free to tell me, and they might work their way into the story. No future is set in stone, after all.

~Neko