DISCLAIMER: The world and characters of Harry Potter belong to their wonderful creator, J.K. Rowling. The world and characters of Calvin and Hobbes belong to the genius known as Bill Watterson. I thank them both for their parts in making my childhood as fantastic as it was.

Chapter One - Not Sending Yourself Letters: A Guide

"Are you sure you didn't send this?" Calvin peered at his best friend accusingly.

Hobbes laid his arms out in front of him, paws up, as if to say 'nothing to hide here'. "Even if I had, you know I would've used cut-out letters from magazines, so that it couldn't be traced back to me."

Calvin nodded grudgingly. "And there's no cool skull icon where the stamp's supposed to be…" He trailed off as he turned the letter over in his hands. "In fact, there isn't anything where the stamp's supposed to be. It's addressed to my bedroom, too. Accurate."

Leaning over to get a better look, the tiger examined the front of the mysterious letter. "Gosh, I've never seen ink so shiny and...green, before. Who do you think would send you a letter, anyway?"

"What's that supposed to mean! Important people send me letters all the time - I just don't let you know about them because then you'd be jealous."

"Pthbt," Hobbes replied, rolling his eyes. "Sure, sure."

"Hey, wait a minute!" Calvin pointed at his furry friend, eyes narrowed. "You're the only one who'd know where my bedroom is that would send me a letter! You did send it!"

"So you admit that no one else would ever send you a letter, ha!"

"You mangy, flea-ridden-"

Hobbes gasped. "Oh you did not just-"

"-sorry excuse for a-"

"Oh you are in for it, buddy!"

"-friend," Calvin finished, glaring at Hobbes.

Hobbes stopped mid-lunge and furrowed his brow. "Oh, I guess that's all right." He folded his arms matter-of-factly. "It really wasn't me, though."

"Wait, what did you think I was going to say," Calvin asked, confusion written across his face in large, neon letters blinking fast enough to give anyone a seizure.

"Tiger."

"...You are a tiger."

Hobbes sighed. "A mangy, flea-ridden, sorry excuse for a tiger."

"So you admit it, ha!" Calvin quickly turned to run as Hobbes' expression darkened. "Sorry excuse for a tiger, sorry excuse for a tiger," he sang as he rounded the corner and headed towards the stairs.

"Oh no you don't, you booger-brained scaredy cat!" Hobbes careened around the corner and lept for Calvin, knocking him down the few stairs he'd since climbed. Their brawl quickly transformed into a cloud of sound effects and insults, with the occasional arm, leg, fist, paw, and tail protruding for a few seconds before being dragged back in.

"Help, I'm being mauled by a kitten!"

"You're one to talk, Mr. I-Might-Be-Eleven-But-My-Shorts-Still-Reach-My-Ankles!"

"Caterpillar butt!"

"THAT WAS ONCE!"

Just then, Calvin's mother poked her head through the nearest doorway, eyebrows drawn into a wide V. "Calvin, if I have to tell you one more time not to roughhouse inside…"

"But mom, it's called roughhouse, not roughbackyard! And it was this letter's fault - we were trying to figure out who sent it, and I thought it was Hobbes." Calvin uncrumpled the offending letter from his clenched fist, and halfheartedly smoothed it out a bit before handing it to his mother.

His mother took the letter, noticing the lack of both a stamp and a return address. "Calvin, I've told you before, if you're going to send yourself letters, you're going to get letters. Now go outside if you have to continue playing so loudly, I've got to finish preparing dinner." And with that, the notoriously skeptical Queen of the Narbogz placed the letter back in Calvin's hand and pivoted, heading back to the kitchen from whence she came.

"Typical Narbogz," Calvin muttered, plopping himself down on the bottom step of the staircase.

"It can only lead to their own downfall," Hobbes sympathized, joining Calvin on the steps. "Open it up already, I want to see who would actually send you a letter."

"Me too," the boy agreed excitedly, ripping apart the envelope like the wrapping paper of a Christmas present being opened way too early on Christmas morning. The paper inside was weird, less like regular paper and more...parchment-y. The same emerald green ink graced the surface, flowing cursive letters making it almost impossible to read. "Who even writes in cursive anymore? I haven't used it since third grade!"

"Maybe it's a third grader," Hobbes supplied. Calvin looked at him dubiously. The tiger shrugged. "Seems like the kind of prank you used to pull back then."

"Oh come on, my pranks were way more imaginative!" complained Calvin, slightly affronted by his friend's accusation.

Hobbes just smiled. "And involved way more water balloons, too." Calvin grinned, then turned back to the letter.

"Hogwarts School of Witchcraft and Wizardry," he read out loud.

"This is one well-done prank, I'll say," Hobbes interjected. Calvin ignored him in favor of continuing to read.

"Headmaster: Albus Percival Wulfric Brian Dumbledore (Order of Merlin, First Class, Grand Sorcerer, Chief Warlock, Supreme Mugwump, International Confederation of Wizards)." He stopped and took a much needed breath. "Wow, that is quite the title. Of course, I still prefer-" Here Calvin cleared his throat and spread his arms out, sweeping across the space in front of him as if announcing a headline. "Calvin: Boy…" He paused dramatically. "...of Destiny. Just as impressive, and a lot easier to remember. I wouldn't mind being a chief of something, though." Calvin tapped his chin thoughtfully. "Being supreme sounds cool, too, but who wants to be in an order? And a class?" He shuddered. "I don't want to hear about class until after summer break - and preferably not even then. This guy does sound impressive though. I wonder what he did to get all the fancy titles. How do you become a master head? I mean, I'm pretty good at using my head, if only as a bumper when I fall down the stairs, which I haven't actually done in a while, come to think of it…" He looked at Hobbes, who had been oddly silent the entire time. "Are you okay, Hobbes?"

The full-grown tiger sat still for a moment longer, before slowly turning to the eleven-year-old boy sitting next to him on the stairs. He stared at him in silence for yet another moment, face twisted in confusion. Then he twitched and exploded in outrage. "What in the world is a Mugwump!?"

Calvin gave his patented shrug and answered, "Sounds like an enemy of the Narbogz. If so, I really wanna meet this guy!"

"Oh, that's okay then. What's the rest of the letter say?"

"Oh, right! Let see, Hogwarts, Brian, Confederation- ah, here we were:

Dear Calvin,

We are pleased to inform you that you have been accepted at Hogwarts School of Witchcraft and Wizardry. Please find enclosed a list of all necessary books and equipment.

Term begins on September 1st. A school representative will be by shortly to answer any questions you may have.

Sincerely,

Minerva McGonagall,

Deputy Headmistress." Calvin frowned. "What is it with the 'head' this and 'head' that - we get it, these people have heads!"

"Did you miss the part where you were invited to a school for wizards?" Hobbes asked incredulously.

"I was WHAT!?" Calvin did a picture-perfect double take and quickly grabbed the letter from where he'd set it down on the step, eyes zooming back and forth as he re-read it. Hobbes just leaned on his arm and sighed. "Hobbes!" yelled Calvin when he'd finished. "There's a school for Witchcraft and Wizardry! And they want me to come!"

"Heaven knows why," the amused tiger muttered, watching his friend's eyes keep on widening. "You'd they wouldn't want to equip the world's most deranged eleven-year-old with more tools of mayhem."

"I wonder if I'll have to do homework," Calvin speculated.

Hobbes plucked the letter from his friend's surprised fingers and looked it over. "Say, when did we stop treating this like a prank and start actually believing that this is all for real?"

"Probably when we found out how many titles that Headmaster guy has."

"It is pretty impressive."

Calvin nodded in agreement. "Plus, when did something being absurd ever stop us from believing in it?" He grinned. "Man, magic, huh? Wonder what mom'll say. Bet she won't believe it."

"She still thinks you sent this letter to yourself," Hobbes pointed out.

"Right. Well, when this representative person comes to answer my questions, they can tell mom."

"Sounds like a plan. What do we do until then?"

Calvin gave a wide grin. "The same thing we do every time we know someone's coming, Hobbes."

The tiger smiled, his feline canines glinting in the artificial lighting of the house. "Water balloon time," he hissed mischievously.

SplashCRACK

"Huh." Hobbes stared down from the bedroom window, watching the wet pavement in front of the door of the house as the water spread.

"Well that's never happened before," Calvin said curiously, studying the same section of wet pavement. There was no one in sight. Which was decidedly strange, as just a moment before there had been an oddly dressed woman with a pointy green wizard's had standing directly below them, about to knock on the front door. "Do you think we've killed her?"

"We? I didn't do anything, you were the one who threw a magic water balloon at her that apparently made her disappear," Hobbes said as if stating the obvious.

"Well standing by and watching would make it assisting a murderer, wouldn't it. And it was a regular water balloon, I swear!" The boy bit his bottom lip nervously. "Now how am I going to convince mom to let me go to Hogwarts School of Witchcraft and Wizardry?"

CRACK-"AHHH!" The two practically jumped out of their skin as the sound of a gunshot blasted into existence directly behind them. They whirled around, tripping over each other, sure they were being attacked by aliens.

"My goodness, boy," said the green-clad, pointy hat-wearing woman harshly in a thick Scottish accent. "I don't think I have ever seen such, such...such Gryffindorish action taken by a muggleborn on the first visit! Why, if term had already started, you would have lost your house a number of points already! Oh, I forgot to introduce myself - I am Professor McGonagall, a teacher at Hogwarts." She seemed quite put-off, but, surprisingly, wasn't dripping wet.

"Why aren't you dripping wet?" asked Calvin, looking up at her. "And how'd you get inside my bedroom? And why did you disappear when the water balloon hit you? And how did you know where my bedroom was? And why didn't you put a skull on the letter, and how do I get cool green ink like that, and what kind of paper did you use, and why are you called a Headmistress and what is a Headmaster?"

The woman looked down at him with a kindly smile. "Magic, Mr. Calvin."

His eyes widened, and his expression was one of complete wonder and admirati- "Wait, that can't be the answer to all of the questions I asked," Calvin said confusedly, interrupting his own narration. "I mean, okay, you aren't wet because of magic, you got here by magic, you disappeared by magic, you knew where my bedroom was because of magic, maaaybe magic is why you didn't put a skull on the letter though I doubt it, it's entirely reasonable to believe that I can get cool green ink by magic but I bet there are other ways too, there's a chance the paper was magic, if you are called Headmistress because of magic that's a weird title, and finally given that I know 'Headmaster' is one of the many, many titles of esteemed Mugwump Albus Percival Wulfric Brian Dumbledore it would be unlikely that a Headmaster is 'magic' otherwise every wizard would have the same title." Calvin had been counting off on his fingers, and breathed a sigh of relief that he still had a thumb left and hadn't had to resort to using his toes, as he was wearing socks - and stopping in the middle of a quick-fire rant to take off one's socks just ruins the moment.

Professor McGonagall peered at him with a bemused expression, as if the situation was only slightly more absurd than what she was used to dealing with. "Are you quite finished yet, Mr. Calvin? I don't have much time, and I really must speak with your parents to make make sure everything is taken care of. If you would follow me." With that she turned on her heel and exited Calvin's bedroom. He could hear her rather loud and intimidating footsteps as she headed downstairs.

"I think she's on to you, buddy," Hobbes said, crawling onto Calvin's bed and curling up, his tail laying itself across his paws.

"What do you think you're doing?"

"Not going downstairs, obviously. That woman scares me - she wasn't even slightly flustered!"

"Well I don't want to face her alone!" whined Calvin. He continued to plead with Hobbes for a few more seconds before he heard a knock at the front door. They met each other's eyes and tilted their heads in question. "I wonder who that could be," Calvin said, getting up from where he was kneeling by the bed and going to stick his head out the window.

"Well?" Hobbes was staring at Calvin's back, looking bored but curious.

"It's Professor McGonagall," answered Calvin, surprised. "But why's she back outside?" He turned to his furry friend, but Hobbes just yawned and stretched before curling up again, this time under the covers. "Fine, stay here you big lump. I'm going to go let her in." He descended the stairs quickly, but by the time he arrived the front door was already opened, and his mother was already standing there looking puzzled.

"-esenting the finest wizarding school in Britain," Calvin heard Professor McGonagall say as he walked up to his mother.

His mother inclined her head suspiciously. "Did you say wizarding? And why would a school from Britain be sending a representative to America? Especially to our house."

"Hey!" exclaimed Calvin, hands on his hips. "I resent that statement!" Then he turned his head to the Scottish woman wearing green. "Why did you go back outside and knock?"

"Back outside!?" his mother asked loudly, looking back and forth between the oddly dressed woman in the pointy hat and her eleven-year-old son.

"Because it is good manners, Mr. Calvin," replied Professor McGonagall sternly. "Something you had better learn if you are going to end up in my house, which, unfortunately for everyone, I am quite certain you will."

"How do you know his name?" said Calvin's mother sharply. "And how did you get inside before if I don't remember ever meeting you?"

"Magic," Calvin said matter-of-factly. His mother, utterly baffled, looked to the woman standing in her doorway. Professor McGonagall nodded in agreement.

"...Magic," his mother deadpanned. "Calvin, is this one of your pranks?" She turned to her son, ready to reprimand him.

"I assure you," the Scottish professor began, holding out a hand placatingly, "this is no prank. Calvin is a wizard, and Hogwarts has invited-"

"Calvin is a what!?" his mother yelled, incredulous.

"Not a what, mom, a wizard," replied Calvin helpfully.

His mother looked at her son, then at Professor McGonagall. "You really expect me to believe that my son is a wizard?"

"Expect the unexpected, that's what I always say," Calvin piped up.

"No you don't," interjected Hobbes, walking up to him. "You always say 'unexpect the expected,' not that it makes any sense."

Calvin raised an eyebrow - he'd had to practice that in the mirror for years - and said, "I thought you were going to stay upstairs?"

"Well there was hardly any chance that I was going to be able to fall alseep with all the yelling going on down here, was there?" shot back Hobbes, waving him off. "Besides, if she's going to do some magic to prove it to your mother, I want to see." Calvin shrugged. He did want to see some magic. Well, more magic.

"Would it be satisfactory if I were to perform some magic to convince you?" Professor McGonagall inclined her head to Calvin's mother, waiting for an answer. His mother glanced at him, then nodded. "Very well. Stand back, then." And right there, Professor McGonagall turned into a cat.

Hobbes hissed and jumped two feet in the air, and when he landed his fur was standing on end, his tail was stick straight, and his back was arched.

"Woah, Hobbes, calm down!" Calvin rushed over to his best friend and tried getting him to stop hissing and eyeing the McGonagall-turned-cat predatorially.

Calvin's mother, on the other hand, was just staring at the feline in shock. She was so shocked that when, in the very next moment, the McGonagall-turned-cat turned back into Professor McGonagall, she didn't react all.

With Hobbes finally calm, or at least calm enough and not thinking about trying to devour the Hogwarts professor, Calvin turned back and started clapping enthusiastically. "That was amazing!"

Professor McGonagall adjusted her glasses. "Well, thank you, Mr. Calvin."

"That was just incredible! It reminds of this one time when I turned into a tiger, except that first I became a slug, then a toad, then something else I think but I forget what, and even after when I was a tiger it wasn't all that awesome and I wasn't ferocious like Hobbes and I have to take a breath now." He took a deep breath and heard Professor McGonagall chuckling quietly. "How did you even do that?"

"Magic."

"SO. COOL." He turned to his mother, who still hadn't reacted at all. "So can I go, mom? Pleeeeaaaase? I'll be extra good and I won't jump out of any windows or eat my hall passes or insult everyone during show-and-tell or refuse to come in after recess or write about my classmates being eaten by velociraptors or just stare blankly at the chalkboard the entire day!"

His mom blinked, and seemed to return to reality. Professor McGonagall, meanwhile, whose eyes had kept widening with each new fact, turned to her in disbelief. "None of those things actually...happened...did they?" she asked hopefully. His mom swallowed and regarded the woman who had just turned into a cat and then back again.

"Take him. Please."

AN: My brain just would not shut up about how awesome it would be for Calvin to meet McGonagall. It was a lot of fun writing this chapter. If you liked it, please review!